School Science Lessons
2024-06-04
Molecular motion Diffusion, particles of matter, Flotation, Hydrometers, Siphons, Archimedes' principle
(UNPh10)
Contents
10.6.0 Archimedes
10.1.0 Diffusion, particles of matter
10.3.0 Flotation
10.2.0 Hydrometers, relative density, RD
10.4.0 Siphons (syphons)
10.1.0 Diffusion, particles of matter
10.1.1 Diffusion experiments
10.1.2 Diffusion in liquids, K manganate (VII) or K dichromate
10.1.3 Diffusion of ammonia and hydrogen chloride gases
10.1.4 Diffusion of carbon dioxide
10.1.6 Graham's law of diffusion
10.2.0 Hydrometers, relative density, RD
10.2.1 Hydrometers
10.2.2 Alcohol meters
10.2.3 Drinking straw hydrometer
10.2.4 Hare's apparatus
10.2.5 Nicholson hydrometer
10.2.6 Relative density, RD., Specific gravity, SG
10.2.7 Relative density of liquids, using relative density bottle
10.2.8 Triple scale wine hydrometer
10.3.0 Flotation
10.3.01 Flotation
Floating, (Primary)
10.3.1 Float different kinds of wood
10.3.2 Float eggs in water
10.3.3 Float grapes at different levels in water
10.3.3a Float ice cubes
10.3.4 Float iron ball in mercury
10.3.5 Float lighted candles
10.3.6 Float metal boats, Plimsoll line
10.3.7 Float needles on water
10.3.8 Float razor blades on water
10.3.9 Float cork, wax and wood in different density liquids
10.3.10 Float corks in a glass jar
10.3.11 Float oil spheres
10.3.12 Float oranges
10.3.13 Floating, sinking and rising under liquid
10.3.14 Floating square bar
10.3.15Weight of a floating body
10.4.0 Siphons (syphons)
10.4.1 Siphons
10.4.2 Cartesian diver
10.4.3 Cold air is heavier than warm air, inverted paper bag balance
10.4.4 Different siphons
10.4.5 Diving bell
10.4.11 Flask fountain
10.4.6 Mariotte bottle (Mariotte flask, Mariotte siphon)
10.4.7 Plastic syringes and air pressure
10.4.8 Self-starting siphon, self-siphoning beads, self-siphoning gel
10.4.9 Siphon fountain
10.4.10 Turnover siphon
10.1.1 Diffusion experiments
Diffusion is the mutual penetration of molecules of substances in contact.
In diffusion, the molecules of a substance in permanent motion, penetrate into the spaces between the molecules of another substance, which is in contact with the first substance, and are distributed among them.
Molecular motion causes the concentration of a substance in an in heterogeneous material to become homogeneous.
Diffusion always occurs from high concentration to low and diffusion occurs at a faster rate when the difference between concentrations is larger.
The smaller the molecules, the faster the rate of diffusion.
The rate of diffusion increases with temperature.
Diffusion occurs in all the states of aggregation, but to different extents.
You can observe diffusion in gases easily.
Diffusion in liquids occurs at a much slower rate than in gases.
Diffusion in solids occurs at a still slower rate than in liquids.
Open bottles of perfumes or other aromatic substance at the end of the room with all windows and doors shut.
Note when you can first smell the substances and estimate the rate of diffusion in air per metre at that temperature.
10.1.2 Diffusion in liquids
See diagram 10.1.3: Diffusion in liquids
1. Place a crystal of potassium dichromate, potassium dichromate (VI), or ammonium dichromate at the bottom of a beaker of water.
To do this, put a glass tube into the beaker of water so that it touches the bottom, then to drop the crystal down the tube.
Close the top of the tube with your finger and remove the tube gently, leaving the crystal in the beaker.
The colour of the dissolving crystal will spread throughout the water in quite a short time.
2. Fill a very small open bottle with a strong solution of potassium permanganate, potassium manganate (VII).
Place this in a larger jar.
Fill the larger jar very carefully by pouring water down the side until the water level is above the top of the small bottle.
Leave this for a few days.
The potassium permanganate solution diffuses evenly through the water.
3. Use two beakers containing water at 90oC and at room temperature.
Put the same quantity of potassium dichromate crystals into each beaker.
Note in which beaker the rate of diffusion of potassium dichromate in water is faster.
Use a glass tube opened at both ends.
Close one end with a stopper.
Then place the tube in water, the open end up.
Put potassium dichromate crystals in the glass tube then gently tap it so that all the potassium dichromate falls to the bottom.
Hold the glass tube in a beaker of water with your left hand to keep it upright and not touch the bottom.
With the right hand, hold a glass rod, longer than the glass tube, in a vertical position, so you can push down on the cork and remove it from the glass tube.
Note how the colour produced by the dissolving crystals of potassium dichromate diffuse through the water.
Fill a small bottle with potassium permanganate solution then put it in an empty beaker.
Fill the container with water so that the water surface just reaches the top of the bottle.
After some days the potassium permanganate solution diffuses completely through the water.
4. Use forceps to place a crystal of lead nitrate and a crystal of potassium iodide in a Petri dish of deionized water.
Observe the crystals dissolving then forming a yellow lead iodide solid between them.
The solid forms closer to the lead nitrate crystal, because the iodide ion moves the fastest.
PbNO3 + KI --> KNO3 + PbI
10.1.3 Diffusion rates of ammonia and hydrogen chloride gases
See diagram 10.1.2: White ring of ammonium chloride
Be careful! Only teachers should do this experiment, because HCl solution and ammonia water are strongly corrosive solutions.
1. Use a long horizontal glass tube with stoppers fitted at both ends.
Use tongs to dip one piece of cotton wool into concentrated hydrochloric acid and another piece into concentrated ammonia solution.
Drain off excess liquid.
Simultaneously, put the soaked pieces of cotton wool inside the ends of the glass tube.
Close the ends of the glass tube with the stoppers.
Watch for a white ring forming where the ammonia gas and the hydrogen chloride gas meet after diffusing through the air towards each other.
Ammonia is less dense than hydrogen chloride, so the white ring of ammonium chloride should form nearer to the hydrogen chloride end of the glass tube.
2. The long glass tube should be horizontal.
Corks should fit at both ends.
Using a pair of tongs or tweezers, dip a piece of cotton wool into concentrated hydrochloric acid and dip another piece into concentrated ammonia solution, (NH3) (aq) ("ammonium hydroxide") solution.
Drain off excess liquid.
Simultaneously, put the ammonia in cotton wool in one end of the tube and the acid in cotton wool in the other end.
Close the ends of the tube with corks.
Later, look for a white ring that will form where the ammonia gas and the hydrogen chloride gas meet after diffusing through the air towards each other.
Ammonia is the less dense gas and the white ring of ammonium chloride should form nearer to the hydrogen chloride end than from the ammonia end of the tube.
3. Different gases diffuse at different rates at the same temperature.
Use glass tube 1 metre long and 2 cm diameter, open at each end, two stoppers, two identical balls of cotton wool, hydrochloric acid, ammonia, water.
Place the glass tube flat on a table.
Immerse one cotton wool ball in hydrochloric acid solution.
Immerse the other cotton wool ball in ammonia solution.
Take them out of the solutions and press them until no liquid drops.
Insert the cotton wool balls into each end of the glass tube simultaneously and instantly insert the stoppers so that air cannot enter the tube.
Observe the position of the white circle band of ammonium chloride formed by diffusion of two gases.
Ammonia molecules diffuse at a faster rate than hydrochloric acid molecules so the two kinds of molecules do not meet at the middle of the glass tube.
10.1.4 Diffusion of carbon dioxide
See diagram 9.154: Limewater test for carbon dioxide in the breath
See diagram 3.55.1: Diffusion of heavy carbon dioxide gas upwards
1. Fill a jar with carbon dioxide and invert it over a similar jar full of air.
After a few moments, separate the jars, pour a little limewater in the lower one and shake it.
The limewater will turn milky indicating that the carbon dioxide has fallen into the lower jar, because it is the heavier gas.
2. Repeat the experiment with the carbon dioxide in the lower jar and invert a jar of air on top of it.
If the jars are left for 5 minutes carbon dioxide will be carried into the upper jar by diffusion, in the same way air will be carried into the lower jar.
The limewater test will show the presence of carbon dioxide in the upper jar.
3. The molecules of gases are always in a random motion.
They may not only move downwards under the gravity to form distribution according to concentrations, but also diffuse in every direction.
Use a wide and thin test-tubes so that the thin test-tube just fits into the wide test-tube.
Fill the thin test-tube with carbon dioxide gas and fill the wide test-tube full of air.
Insert the open end of the thin test-tube into the wide test-tube.
Let them stand vertical.
After some minutes, separate them quickly.
Add some limewater into the wide test-tube and shake it gently.
Note the change in colour.
The solution changes from clear into muddy and finally becomes milk white.
It shows some carbon dioxide gas has entered the thick test-tube, because denser carbon dioxide molecules go down from the thin test-tube into the wide test-tube under the effect of gravitation.
4. Fill the wide test-tube with carbon dioxide gas and inflate the thin test-tube full of air.
Insert the open end of the thin test-tube into the wide test-tube and let them stand vertical.
After some minutes, separate them then quickly add some limewater into the thin test-tube and shake it gently.
Observe the change in colour at the thick one.
The solution changes from clear into muddy and becomes milk white liquid finally.
It shows some carbon dioxide gas has entered the thin test-tube, because carbon dioxide molecules in random motion diffuse in various directions, including upward and downward.
So some carbon dioxide molecules go up from the thick test-tube into the thin test-tube.
10.1.5 Diffusion rates of ammonia and hydrogen chloride gas
See diagram 3.55.2: A diffusion race, A concentrated HCl in cotton wool, B concentrated ammonia solution in cotton wool
Use a long horizontal glass tube with stoppers fitted at both ends.
Use tongs to dip one piece of cotton wool into concentrated hydrochloric acid and another piece into concentrated ammonia solution.
Drain off excess liquid.
Simultaneously, put the soaked pieces of cotton wool inside the ends of the glass tube.
Close the ends of the glass tube with the stoppers.
Watch for a white ring forming where the ammonia gas and the hydrogen chloride gas meet after diffusing through the air towards each other.
Ammonia is less dense than hydrogen chloride so the white ring of ammonium chloride should form nearer to the hydrogen chloride end of the glass tube.
10.1.6 Graham's law of diffusion
The rates of diffusion of particles of gas are inversely proportional to the square root of the molar mass of the particles.
Rate of diffusion A / Rate of diffusion B = √ molar mass B / √ molar mass A
10.2.1 Hydrometers
See diagram 11.3.2: Simple hydrometer
Hydrometers include test-tube hydrometer, battery acid hydrometer, food testing hydrometers, constant weight hydrometer, constant volume hydrometer, and the Nicholson hydrometer and Mohr-Estphal balance are used with liquids of various density.
A hydrometer is a device for measuring the specific gravity of a liquid relative to water, specific gravity of 1.0 measuring the density of the liquid in grams per cubic centimetre.
10.2.2 Alcohol meters
Alcohol meters, used by excise officers in the customs service are used to determine the percentage by volume of alcohol in a given sample of alcohol-water.
Each alcohol meter covers a particular range of values and is direct reading to 0.2 %, read from the engraved marks on the stem.
The glass bulb is weighted with lead shot.
To determine the percentage by volume of alcohol (ethanol) in a particular, e.g. rum, an alcohol value obtained from the rum itself would not truly indicate the alcohol content, because it would be affected by various other substances e.g. sugars in solution.
So a sample of the rum is diluted with water and distilled until all the alcohol and some water has been collected as a distillate.
The hydrometer is then placed in the distillate, of which there must be sufficient volume to give a depth in which the hydrometer can float.
A 1000 mL measuring cylinder is commonly used, as the hydrometers are approximately 30 cm in length.
A thermometer is also placed in the distillate and readings noted.
From comprehensive tables that convert an observed alcohol percentage at a given temperature to the percentage at 20oC, the legally defined value is obtained.
For example, from a table of the concentration by weight of an ethanol-water mixture vs specific gravity at temperature:
At 25oC, Weight % alcohol, Specific Gravity, 0% 0.99708 (pure water), 10% 0.998043, 15% 0.97334, 50% 0.90985, 70% 0.86340, 100% 0.78506.
The specific gravity of ethanol is 0.79.
10.2.3 Drinking straw hydrometer
1. Seal one end of a drinking straw.
Put some sand in it until it floats in water in a vertical position.
Put a rubber band round the stem so that you can slide it up and down as a marker.
Mark the drinking straw at water level.
Measure the length from the bottom end of the drinking straw to the water level mark, X cm.
Assume the relative density of water = 1, and assume that the drinking straw has a uniform cross-section area.
Mark the drinking straw for different relative densities, e.g. from 0.6 to 1.2.
Check the accuracy of your drinking straw hydrometers with a glass hydrometer.
2. Put a drinking straw hydrometer in water, then put it in alcohol.
Show the buoyancy of hot and cold water with a hydrometer that floats lower in warm water and higher in cold water.
10.2.4 Hare's Apparatus
See diagram 11.3.4: U-tube and Hare's apparatus
Hare's apparatus (Robert Hare, l781-1858, USA) has an inverted U-tube with outlet tube at the top.
Beakers of water and another liquid can be placed under the two ends and some air withdrawn through the outlet in the bend so columns of liquids would rise in the arms.
Show how to find the relative density of a liquid.
With the Hare's apparatus assembled and liquids in the beakers, withdraw air to obtain convenient heights of liquids in the arms.
Adjust volumes in the beakers to bring both liquids to the same horizontal level.
The density of one liquid relative to the other is given by the appropriate ratio of the column heights.
10.2.5 Nicholson hydrometer
See diagram 11.3.2.1: Nicholson hydrometer
1. Nicholson hydrometer has a submerged pan for determining the specific gravity of solids by weighing them both in water or any other liquid and in air.
It has a hollow cylindrical body, usually 15 cm in length, with tapered ends and is sealed be water tight.
An upper platform can carries small objects or standard masses.
A lower platform also hold objects.
The sealed conical base of the lower platform contains a lead shot, to give the whole device a sufficient weight so as to sink to a convenient depth in liquids.
The stem connecting the upper platform to the top of the body carries an engraved mark, to which the hydrometer is always sunk when in use.
Put it in water and load small weights on the platform until the water level reaches a mark on the wire stem.
Then put the hydrometer in the unknown liquid, and add weights to the platform until the same mark on the wire stem is reached.
Calculate the relative density of the unknown liquid knowing the mass of the hydrometer and the value of the two sets of masses used to bring the hydrometer to the reference line.
2. Nicholson hydrometer
True specific gravity of a solid
The Nicholson hydrometer is floating with the mark on the stem just below the surface so adjust weights so that it floats exactly with the engraved mark at the surface = 8.345 g added to top pan.
Remove the weights and put the solid on the top pan.
Add weights until the mark again comes to the surface = 2.539 g
So the weight of the solid in air is the difference = 8.345 - 2.539 = 5.806 g
Put the solid in the lower cup and put weights on the top pan until the mark sinks to the surface = 5.462 g
The weight of the solid in water = 8.345 - 5.462 = 2.883 g.
The weight of water displaced = (weight in air - weight in water) = (5.806 - 2.883) = 2.923 g.
The specific gravity of the solid = 5.806 / 2.923 = 1.987.
(Specific gravity is a ratio so there are no units.)
However, this calculation referred to water at the temperature of the experiment when the ambient temperature was 15oC.
To determine the true specific gravity with water at 4 C as the standard, by reference to tables the specific gravity of water at 4 C = 0.99917.
So the true specific gravity of the solid = 1.987 × 0.99917 = 1.985.
10.2.6 Relative density, RD, Specific gravity, SG
Pure water has its highest density 1000 kg/m3 at temperature 4°C (=39.2°F). 1. Relative density, RD, is the ratio of the mass of a volume of a substance with the mass of an equal volume of water at a temperature of 4oC.
It is a physics quantity of no dimension.
For convenience, use this ratio instead of quoting the density, e.g. the density of mercury = (13.6 ×103 kg / m3), so RD. mercury = 13.6.
Specific gravity is the ratio of the density of a substance to the density of a standard substance, usually with water, density 1.000 kg per litre at 4oC, or with dry air density 1.29 kg per litre at 0oC and 1 atmosphere pressure.
Carbon dioxide with density 1.976 g per litre at standard conditions has specific gravity = 1.976 / 1.29 = 1.532.
Specific gravity is a ratio so it has no units.
Relative density was formerly called specific gravity, so SG water = 1.
Specific gravity is still used to measure the concentration of the sulfuric acid electrolyte in a motor car battery, in the brewing industry, and in laws applying to that industry and the processed foods industry.
Specific gravity is a defining characteristic of minerals.
Specific gravity is measured with the hydrometer, Jolly balance, pycnometer, and Westphal balance.
Experiments
2.1 Find the density of a liquid other than water, e.g. methylated spirits, using a density bottle.
Let the weight of the empty bottle and stopper be tared out to zero, and make weighings when a bottle is full of the liquid (w1) and water (w2), relative density of methylated spirits = w1 / w2.
2.2 Find the density of a finely divided solid that is insoluble in water, e.g. sand.
Weight of empty bottle + stopper (w1).
Weight of bottle + stopper + d solid (w2).
Weight of bottle + stopper + solid + water filling the bottle (w3).
Weight of bottle + stopper + water filling the bottle (w4).
Relative density of solid = (w2- w1) / (w4 - w1) - (w3 - w2).
2.3 Find the density of a solid that is soluble in water, e.g. cane sugar.
Repeat 2.2 using mineral turpentine instead of water to give the density, d1 relative to mineral turpentine.
To find the density of mineral turpentine repeat 2.1 using mineral turpentine.
Density of sugar relative to water = d1 / d2.
2.4 Find the density of an insoluble solid, more dense than water, e.g. lead.
Weight of lead sample suspended in air, w1.
Weight of lead sample suspended in water, w2.
Relative density of lead sample = w1 / (w1-w2).
2.5 Find the density of an insoluble solid, less dense than water, e.g. candle wax.
Weight of wax sample in air, w1.
Attach wax sample to a lead sinker with a string.
Weight of lead sinker submerged in water with wax sample above the water, w2.
Weight of lead sinker and wax sample both submerged under water, w3.
Relative density of wax sample = w1 / (w2-w3).
2.6 Find the density of a liquid other than water, not using a density bottle.
Weight of a lead sinker attached to string in air, w1.
Weight of a lead sinker attached to string in methylated spirits, w2.
Weight of a lead sinker attached to string in water, w3.
Relative density of methylated spirits = (w1-w2) / (w1-w3).
10.2.7 Relative density of a liquid, using a relative density bottle
See diagram 11.2.0: Density bottle
Use a beam balance to measure the mass of a relative density bottle (specific gravity bottle), which has an accurately known volume, usually 50 mL.
Experiment
Weight of the bottle = m1.
Fill the bottle with a liquid whose density is unknown and insert the stopper.
Wipe dry the surface of the bottle.
Weight of the bottle + unknown liquid, m2.
Density of liquid = (m2 - m1) / v, where v = volume of the bottle.
Pour the liquid out of the bottle then clean the bottle.
Fill the bottle with water and insert the stopper.
Weight of the bottle + water = m3.
Calculate the relative density of a liquid.
Density of liquid = (m2 - m1) / v, density of water = (m3 - m1) / v.
Density of a liquid relative to water = ([m2- m1] / v) / ([m3 - m1] / v).
So the relative density of a liquid, RD = (m2 - m1) / (m3- m1).
10.2.8 Triple scale wine hydrometer
From Tony at DDMETER CO., LIMITED.
Homebrew hydrometers:
1. Triple scale hydrometer: (colour scale &instruction; Sturdy packaging)
Specific Gravity: 0.990 – 1.160, Potential Alcohol: 0%-20%, Brix/Balling: 0-35
2. Proof and Tralle Hydrometer
0-200 proof, 0-100% alcohol
See diagram 11.3.2: Wine hydrometer
By using this hydrometer you can follow the process of fermentation.
As yeast converts sucrose sugar into ethanol the specific gravity of the juice of the crushed grapes, a called the "must or wort", decreases and the hydrometer sinks until fermentation is complete.
If you put wine SG > 1.006 into bottles, the fermentation is incomplete and the bottles may burst from the extra carbon dioxide produced in the bottle.
To test the specific gravity of the "must", use a plastic tube to siphon off a sample of the liquid.
Put in the hydrometer so that it floats freely.
Use your thumb and first finger to spin the hydrometer to spin off any bubbles clinging to the surface of the hydrometer.
When the hydrometer stops spinning and does not touch the sides of the container, read the upper meniscus.
The hydrometer will be calibrated to give correct readings at a certain temperature, e.g. 20oC.
For other temperatures, you must apply a correction to the final specific gravity reading, e.g. 10oC (- 0.002), 15oC (- 0.001), 25oC (+ 0.001), 30oC (+ 0.003), 35oC (+ 0.004).
Estimate the percentage alcohol content by measuring the specific gravity before and after fermentation, based on the fact that 2.7 g of sugar gives 1 hydrometer degree in 1 litre of liquid and 17 g of sugar, gives 1% of alcohol in one litre of wine.
The wine hydrometer has its own container of known volume so besides a specific gravity scale it can also have a scale to estimate the percentage alcohol content if all the sugar is converted into alcohol.
If initial specific gravity before fermentation = 1.090, then potential percentage alcohol by volume = 11.8%.
If final specific gravity = 1.010 after fermentation, then potential percentage alcohol by volume = 1.3%, the fermentation has stopped.
So alcohol contents = (11.8 - 1.3) = 10.5%.
Also the hydrometer has a scale to estimate how much sugar to add to give a required alcohol content.
So the triple scales are as follows:
1. Specific gravity scale, 2. Potential alcohol content scale, 3. Amount of sugar to add scale.
10.3.01 Flotation
An object floats in a liquid when the weight of the body is equal to the weight of liquid displaced.
When an object is placed in a liquid with greater relative density than the object, it will sink until the weight of the liquid displaced is equal to weight of the body.
10.3.1 Float different kinds of wood
See diagram 11.284: Floating wood
1. Put pieces of wood and cork with the same dimensions in a pan of water and note how each piece of wood floats.
Measure the ratios of lengths above and below water.
2. Place lengths of wood with equal dimensions in a graduated cylinder containing water.
Insert a drawing pin (thumb tack) up into the bottom of the lengths of wood to make them float upright.
Measure the ratios of whole length to length below water.
10.3.2 Float eggs in water
See diagram 11.285: Floating egg
1. After the egg is laid and it starts to cool, the air cell forms.
In a fresh egg the air cell is quite small and the egg sinks to the bottom of a container of clean water.
A fresh egg has a thick white that does nor spread out far in the pan and the yolk stands up.
As the egg gets older it loses water by evaporation.
The water is replaced by air so the egg decreases in weight and starts to stand up, smaller end down.
Later the egg starts to rise to the surface of the water.
2. Place an egg in a glass of tap water.
Add salt to the water to increase the relative density of the water make the egg float.
Ships float higher in salt water than in fresh water, because salt water is more dense than fresh water.
3. A floating egg to be used for cooking may be bad, so it should be opened in a separate container and discarded if any bad smell can be detected.
The bad smell comes from hydrogen sulfide, (H2S), (rotten egg gas) produced by the decomposition of proteins in a rotten egg.
Such an egg may contain the dangerous Salmonella bacteria that can cause sickness and death.
So never use floating eggs for cooking!
10.3.3 Float grapes at different levels in water
Be careful! Do NOT taste chemicals in the laboratory.
1. Prepare 4 beakers of water.
Put a grape in beaker 1 then fill the beaker with tap water.
Put a grape in beaker 2, add some tap water then add sugar until the grape floats on the surface of the water.
Prepare beaker 3 in the same way as for beaker 2, then pour out half the water.
Wait until the solution in beaker 3 is still, then very slowly add tap water until the beaker is full.
The grape now floats between the lower sugar in water and the upper pure tap water.
Carefully increase the concentration of sugar in the water, while stirring, until the grape floats at the same level as in beaker 3.
To investigate why the grapes float at different levels, taste the water in each beaker by just touching the surface.
You can taste the difference between beaker 1 and beaker 2, but beaker 3 tastes the same as beaker 1, and beaker 2 tastes the same as beaker 4.
10.3.3a Float ice cubes
1. Observe an ice cube floating in a jar of water.
Fill the jar completely with water and place the jar on absorbent paper.
Measure the proportion of the ice cube above the surface of the water.
Observe the melting ice cube and note any overflow onto the absorbent paper.
Again measure the proportion of the ice cube above the surface of the water.
The water level in the jar does not change as the ice melts.
2. Repeat the experiment with an ice cube floating in salty water.
The ice cube floats higher in the salty water.
Observe any overflow of salty water + ice cube water.
The icebergs that float in the antarctic ocean come from ice formed on the land, so they are composed mainly of fresh water.
The amount of salty sea water displaced by the iceberg is equal to the weight of the iceberg, the volume of melted fresh water will be slightly higher than the displaced sea water, so the sea water level will rise when all the icebergs melt.
3. Float an ice cube in oil over water
Use a glass beaker half full of water and vegetable oil.
Add an ice cube.
Note the level at which the ice floats.
The ice cube should float with the top above the upper level of the vegetable oil, so use a vegetable oil that is dense enough.
Most vegetable oils have density 0.91 - 0.93 g / mL.
The temperature of a melting ice cube is 0oC and the temperature of the oil and water in the beaker is the room temperature, the standard being 25oC.
For this experiment the lower level of the ice cube should be well above the lower level of the vegetable oil, so use sufficient volume of vegetable oil.
Examine the surface of the ice cube as it melts.
Some teachers use ice cubes containing a dye.
The density of the ice is less than the density of the vegetable oil, so when the ice melts the melt water runs down the sides of the ice cube and collects below it as a downwards pointing drop.
As the drop gets bigger, it may weigh down the ice cube.
This water drop remains suspended below the ice cube, because it is covered below by a layer of vegetable oil and sits at the interface between the oil and water.
Eventually, the oil drop becomes so heavy that the water bursts through the layer of oil and, being colder and more dense than the oil and water below, plunges down to the bottom of the beaker.
If a dyed ice cube is used, the water will develop an even colour after some time.
10.3.4 Float iron ball in mercury
See diagram 4.212: Float an iron ball in mercury
Mercury is not permitted in schools except in some school systems where it is allowed only in barometers and thermometers.
However, as this is a famous experiment, it can be taught as a theoretical exercise.
1. An iron ball is floating in a beaker of mercury.
Assume the specific gravity of air = 0, iron = 8, and mercury = 14.
The iron ball floats with 8 / 14 (0.57) of the volume of the iron ball in the lower fluid.
The weight of the iron ball is balance by weight of mercury displaced.
Add water to the beaker to cover the iron ball and mercury completely.
Does the iron ball sink down in the mercury or rise in the mercury or continue with same ratio above and below the mercury?
The short answer is that the iron ball rises in the mercury, because it experiences an extra upthrust equal to the weight of water displaced by the volume of the iron ball above the mercury.
The weight of the iron ball is balanced by the combined weight of the displaced mercury and displaced water.
The iron ball floats with 7 / 13 (0.54) of the volume of the iron ball in the lower fluid.
In this calculation, the specific gravity of air is assumed to be = 0.
However, air does have a small specific gravity, so when we weigh a body on a balance we habitually ignore the upthrust on the body caused by displacement of air.
10.3.5 Float lighted candles
1. Push nails or pins in the lower end of a candle so that the candle floats vertically with its top a little above the surface of the water.
Light the candle and watch it burn.
The candle constantly loses mass as it burns.
The candle continues to float if it displaces a mass of water greater than its own mass.
In floating tea lights, the wick is attached to metal at the base to stop it floating to the top of the molten wax.
Also, the base is sealed to stop the wick drawing up water by capillarity to extinguish the flame.
10.3.6 Float metal boats, Plimsoll line
See diagram 11.211: Plimsoll line
See diagram 4.211: Plimsoll line: LR Lloyd's Register Mark, T Tropical, S Summer, W Winter, WNA Winter North Atlantic, F fresh water, TF Tropical fresh water
1. Shape a piece of aluminium foil into the form of a little boat.
Float the boat on water.
A floating boat displaces the volume of the boat under water.
This volume is greater than the volume of the ball of metal foil.
The weight of this volume of water displaced is equal to the weight of the boat, so the boat floats.
2. Squeeze the metal boat into a ball.
Try to float the ball on water.
The ball sinks.
Buoyancy force = weight of water displaced.
The ball of aluminium foil displaces its own volume of water.
The ball is heavier than its own volume of water, so it sinks.
3. Plimsoll line, Plimsoll mark, load lines
Plimsoll lines (Samuel Plimsoll 1824-1898 England), introduced under the Merchant Shipping Act of 1876, are lines painted on both sides of a ship to show the minimum freeboard, load line, allowed in different parts of the world and at different seasons to prevent dangerous overloading of the ship.
If you live near a sea port, look for the Plimsoll lines on the sides of the big boats.
The water line is the line formed by the surface of the water against the hull of a ship.
The 6 load lines on the Plimsoll mark show the depth to which the ship can be loaded, i.e. the water-line should not be above this line in different conditions, e.g. summer or winter (fresh water or salt water), to allow sufficient reserve buoyancy.
In all countries the load lines show the legal limit of submersion of a ship as administered by various government recognized authorities, e.g. LR, Lloyd's Register of Shipping.
The freeboard is the height of a ship's side between the water line and lowest part of the deck, the line of the weather deck.
So a ship fully loaded in the salty ocean could become dangerously low in the water when it travels up a fresh water river.
Shoes with a canvass upper and rubber sole are called "plimsolls", because the line where the rubber and canvas meet reminds people of the Plimsoll line.
10.3.7 Float needles on water
See diagram 4.213: Float a needle
1. Use a steel needle and dry it thoroughly.
Place it on the tines of a dinner fork and gently break the surface of some water in a dish with the fork.
If you are careful, the needle will float as you take the fork away.
Look at the water surface closely.
See how the surface film seems to bend under the weight of the needle.
2. Float a paper clip on water.
Hold a paper clip in a sling made of a paper towel.
Dip the paper clip on to the water surface.
Take away the paper towel.
See the water surface bending under the paper clip.
3. Float needles, paper clips, rings of wire, and a razor blade on water.
4. Float an aluminium sheet on the surface of distilled water and add weights until the metal sinks.
10.3.8 Float razor blades on water
See diagram 9.8.0: Mosquito larva
Mosquito larva using surface tension of water
Use a razor blade of the double edge type.
Try floating it on the surface of water.
Again note the surface and see the surface film.
10.3.9 Float cork, wax and wood in different density liquids
See diagram 11.287: Floating in different density liquids: A, B, C, D are liquids with increasing density
1. Use a piece of wood that at sinks in water paraffin wax or candle wax and a piece of cork.
Pour water into a measuring cylinder or tall glass jar.
Then carefully pour the kerosene into the jar on top of the water.
Drop in the solid substances.
The wood sinks in two liquids.
The paraffin sinks in the kerosene, but floats on the water.
The cork floats on the kerosene.
Floating condition: if the density of a solid is greater than that of the fluid, then it will sink, if the solid's density is equal to that of the fluid, the solid will float anywhere in the liquid.
If the solid's density is less than that of the fluid, the solid will float above the surface of the liquid.
2. To understand the condition of a solid floating in a liquid, use a thin and tall glass bottle (or a glass test-tube, a glass cup) and liquids with different density, e.g. water, kerosene, honey or molasses.
Solids: a steel ball (e.g. ball bearing), iron bolt or screw, a small block of ebony or other sinkable into water wood block, a piece of solid paraffin, a small cork.
Pour liquids into the glass bottle according to the order of density.
Pour the liquids slowly along the rim of the bottle under a glass stick.
Do not make the surfaces between liquids mix.
Gently put the four solids into the liquid.
Observe the floating in the different layers of liquids with different densities.
3. Float a test-tube in water, kerosene, and a mixed solution of kerosene and water.
4. Fill a test-tube with several immiscible liquids of different densities.
Then add solid objects that will float at the various interfaces.
10.3.10 Float corks in a glass jar
A molecule of water is composed of three atoms: two hydrogen atoms and one oxygen atom.
Because the oxygen atom tends to have the electrons orbit it more than the hydrogen atoms, the oxygen atom has a slight negative charge, and the hydrogen atoms have a slight positive charge.
Because of this property, oxygen is called a polar molecule.
This property also allows the water molecules to form hydrogen bonds with each other, between the positive hydrogen atoms and negative oxygen atoms.
Because the individual water molecules form these hydrogen bonds, water has a very high surface tension.
This high surface tension actually allows the water level to rise up over the mouth of the cup before the water overflows down the sides.
Experiments
1. Half fill a glass jar with water and float a flat cork on the water.
Note where the cork floats.
It floats near or touching the wall of the glass jar.
Add more water to the glass jar until a meniscus forms.
Note where the cork floats.
It floats in the centre of the water surface.
If you push the cork towards the edge of the water surface it returns to the centre.
When the glass jar is half filled with water, the highest level of the water is the circumference of the meniscus due to the adhesive forces between the water and the glass molecules.
A cork floats at the highest place, so it floats at the circumference.
When the glass container is filled with water, the forces of cohesion between the water molecules allow a meniscus to form across the whole surface of the water, like a skin.
As the highest level of the meniscus is now in the centre of the water surface, the cork floats at this highest place.
2. Cut 1 cm diameter circles of polystyrene.
Fill a polystyrene cylinder with water 1 cm from the top.
The polystyrene circles tend to float clumped together, but after weak agitation of the water surface, the polystyrene circles move outwards towards the surface of the container and stay there.
Take out all but one circle of polystyrene and add water to the cylinder or add stones until a meniscus forms.
The circle of polystyrene moves to the centre of the meniscus.
Use a pencil to push the circle of polystyrene away from the centre.
Remove the pencil and it returns to the centre of the meniscus.
The meniscus in the partially-filled container curves up to meet the container sides, because water molecules are more attracted to polystyrene than to each other.
In the over-filled container the water forms a convex bulge, because surface tension constricts the are of the water surface to a minimum.
The water molecules pull evenly on the circle of polystyrene so it remains in the middle of the meniscus.
10.3.11 Float oil spheres
Pour 50 mL water in a beaker.
Hold the beaker in a slant and slowly pour 50 mL ethanol on top.
Leave the beaker to stand.
Fill a dropper with light oil, e.g. olive oil.
Insert the opening of the dropper to where the two liquids meet in the beaker and squeeze out drops of oil.
Withdraw the dropper out of the liquid.
The oil takes the shape of a sphere and stays between the two layers of liquid.
Ethanol has density 0.794 so it can float on water and form a layer.
It is not totally immiscible with water, but when poured slowly it can form a layer and stay above the water.
Where the two liquids meet, the water and the oil mix and form a liquid with a density close to the density of oil so the oil forms a sphere between two liquid layers.
A sphere is formed, because it has the smallest surface area as compared to other three dimensional shapes.
When the beaker is left standing, the alcohol evaporates slowly, and the oil sphere moves up slowly until it reaches the surface and then the sphere slowly becomes a flat circle when all the alcohol has evaporated.
10.3.12 Float oranges
The orange with its peel on floats, because its ratio of mass to volume is less than that of the water.
Removing the peel reduces the volume of the orange and reduces its mass to increase the density of the peeled orange to be greater than water, so it sinks.
Cut the orange in half, to halve the orange's mass and halve its volume, but not change its density so it floats.
Remove the peel and the half orange sinks.
Weigh the orange and measure its volume.
Use a beam balance to compare the mass of the peel and the peeled orange.
Use a spring balance to find the weight of the peel and the peeled orange.
Use an overflow can and a measuring cylinder to compare the volume of the peel and the peeled orange.
Calculate the density of the orange, the peeled orange and the peel.
10.3.13 Floating, sinking and rising under liquid
Floating is state of equilibrium in which an object rests on or suspended in the surface of a fluid (liquid or gas).
According to Archimedes' principle, an object wholly or partly immersed in a fluid will be subjected to an upward force, or upthrust, an instantaneous upward force, equal in magnitude to the weight of the fluid it has displaced.
If the density of the object is greater than that of the fluid, then its weight will be greater than the upthrust and it will sink.
However, if the object's density is less than that of the fluid, the upthrust will be the greater and the object will be pushed upwards towards the surface.
As the object raises above the surface, the amount of fluid that it displaces (and therefore the magnitude of the upthrust) decreases.
Eventually, the upthrust acting on the submerged part of the object will equal the object's weight, equilibrium will be reached, and the object will float.
10.3.14 Floating square bar
A long bar floats in one orientation in alcohol and switches to another orientation when water is added.
10.3.15 Weight of a floating body
1. Fill an overflow can with water and let it run out until the surface is level with the spout.
Select a piece of wood that floats half or more submerged in the overflow can.
Weigh the piece of wood with a spring balance.
Weigh the catch bucket.
Put the catch bucket under the spout.
Put the wood block in the overflow can and note the balance reading.
Find the weight of the displaced water by subtracting the weight of the catch bucket from the total weight of catch bucket and water.
The weight of the water displaced is equal to the weight of the object.
10.4.1 Siphons
Siphons are pipes or tubes used to move liquids from a higher level to a lower level by using the liquid pressure differential to force a column of the liquid up to an even higher level before it falls to the lower level at the outlet.
* Siphons are tubes used to move liquids from a higher container to a lower container, e.g. siphon gasoline out of a gasoline tank in a motor car.
Pumps are machines used to move liquids or gases.
Atmospheric pressure, not cohesion, is the basis for the siphon action.
* The flow rate is dependent on the height of the loop, not because there is a greater weight of water being pushed up the tube, because there is an equal weight of water on the other side to balance this out.
It is because of the greater length of tube and the greater friction involved in the flow, h2 > h1.
1. You can define the siphon, as a pipe system consisting of two legs as an inverted J, used to carry a liquid from one vessel to another vessel at a lower level, over an intermediate level higher than both levels.
When both legs of the siphon are full, the hydrostatic force due to gravity is larger on the longer leg, thus causing the liquid to move up the shorter leg, over the bend, and down the longer leg.
Start the siphoning process by:
1.1 filling a siphon with liquid before placing it into its operating location, or
1.2 by applying suction at the lower end after the tube is in position.
Once started, the flow will continue until the liquid level in both vessels is equal, or until the level in the higher vessel falls below the inlet of the tube when air is sucked in and the siphoning action stops.
2. There is more than one explanation of how the siphon works
Explanation 1: The forces of cohesion, surface tension between water molecules, allows the water in the short side of the siphon to be pulled up the tube by the greater weight of the water in the long side.
The siphon acts in much the same way as the longer end of a chain hanging out of a bucket can pull the rest of the chain from the bucket.
Explanation 2: Both surface tension and atmospheric pressure are required to make the siphon work.
Gravity pulls down on the water in both sides of the siphon.
However, because there is more water in the long side, the weight is greater in the long side than in the short side.
If the columns of water are not allowed to separate, the water in the long side will pull the liquid up the short side.
Atmospheric pressure keeps the water from separating.
The water flowing down the long side reduces the pressure in the siphon and thus atmospheric pressure pushes water up into the short side of the siphon if it is greater than the pressure of the column of water in the short side of the siphon.
If atmospheric pressure did not exist then there would be no reason for water to enter the short side of the tube.
The following experiment, the siphon fountain, shows that the principle of operation for a siphon does not rely on surface tension alone.
3. After "Understanding the siphon" Kevin C. de Berg and Cedric E. Grieve, Australian Science Teachers Journal, 45 (4)
The explanatory principle based on comparing the weights of fluid in both legs of a siphon occurs in most textbooks analysis and in the work of the French scientist Pascal, 1663.
The advantage of this principle is that it is relatively simple and applies to siphons as commonly employed.
Its disadvantage is are that it applies only to siphons and not other fluid flow devices, e.g. syringes, and applies only where the siphon fluid is more dense than the external fluid.
The following explanatory principle overcomes this disadvantages:
The siphon in Diagram 12.4.05: has a fluid disc of negligible thickness at X.
You can consider the contending pressures either side, S and S1 of this disc at the moment the stopper is removed from X.
The pressure on side S1 is atmospheric pressure, AP.
To locate the pressure on side S of the disc, follow the pressure changes on the other side of the siphon starting at the surface of the fluid in the container where the pressure is atmospheric pressure, AP.
At A, the pressure is (Ap + 2).
At B the pressure is (AP + 2 - 18).
At X, the pressure is (AP + 2- 18 + 6), i.e. (AP - 10).
The pressure on side S1 exceeds the pressure on side S so the liquid will not siphon from the tube, but move back into the longer leg and into the container.
In diagram 12.4.05 2. for this siphon, at X, the pressure on side S1 is again AP.
On side S, the pressure (AP + 2 - 12 + 14), i.e. (AP + 4).
The pressure on side S exceeds the pressure on side S1 and so fluid siphons from the beaker out of the longer leg of the siphon.
The pressures on either side of a fluid disc of negligible thickness at the opening of the needle after the plunger has been moved back, but before fluid has begun to flow.
On side S the pressure is less than atmospheric pressure, because a small sample of air at atmospheric pressure was expanded into larger volume. On side S1 the pressure is (AP + h).
So the pressure on side S1 exceeds the pressure on side S and fluid moves into the syringe from high pressure to low pressure.
10.4.2 Cartesian diver
See diagram 11.280: Cartesian diver
See diagram 4.201: Cartesian diver
Cartesian diver was invented by René Descates (1596 - 1650), France.
1. A simple Cartesian diver consists of a test-tube containing a bubble of air and which floats mouth downwards in a partially-filled cylinder of water closed by an elastic cover, e.g. a rubber sheet.
The diver floats in the water, because the total mass of the glass of the test-tube and the enclosed air is equal to the weight of the water displaced by the glass and air (Archimedes' principle).
When pressure is applied to the cover, it is transmitted undiminished through the air to the water surface and through the water to the air bubble (Pascal's principle).
When the pressure of the air is increased, the volume is decreased (Boyle's law).
Thus the volume of air in the test tube is diminished and so is the volume of water displaced with the result that the weight of water displaced by the diver is diminished.
The downward force equal to the weight of the diver is greater than the upward force equal to the weight of water displaced.
Thus the diver sinks.
2. Wrap copper wire around the narrow part of the rubber bulb from a medicine dropper to make a rubber diver.
Fill a tall plastic container with water.
Put enough water in the rubber diver so that it only just floats in the container of water.
Most of the rubber will be under water.
Adjust how much the rubber diver floats by pinching the bulb to remove air.
Cover the container with a sheet of plastic or rubber and fix it tightly around the rim of the container with string or rubber bands.
Press on the tight plastic cover to make the diver sink.
Stop pressing on the tight plastic cover to make the diver rise.
3. Repeat the experiment using a very small glass tube to make a diver.
Add ink to the water to help you see the water level in the glass tube.
Note that when the cover is pressed down, the pressure is transmitted through the water to decrease the volume of the air bubble in the glass diver.
So the water level rises in the tube.
When the volume of the air bubble is too small to hold up the glass diver by displacement of water the glass diver will sink.
When you stop pressing on the cover, the decrease in pressure is transmitted to the air bubble that expands, so the water level in the glass diver decreases.
The increased volume of the air bubble in the glass diver displaces enough water to provide an upward force by displacement of water to allow the glass diver to float again.
4. Push a wooden match stick into a hollow plastic ball.
The plastic ball by itself just sinks in water, but the match gives it enough buoyancy to just float.
Shorten the match so that its end floats level to the surface of water in a plastic drink bottle.
Close the bottle with a plastic cap.
The pressure of the fingers on the walls of the plastic bottle is transmitted to compress the air in the plastic ball and it sinks.
5. Cut a fresh piece of orange peel in the shape of a submarine.
Make portholes in the side with the end of a ball point pen.
Put the orange peel submarine in a container of water sealed with a plastic cap.
Bubbles in the orange peel allow the submarine to float.
Pressure on the plastic cap is transmitted to decrease the size of the bubbles and the submarine sinks.
6. Use a plastic ball point pen top with a pocket clip.
If air can pass through the upper end seal it with Plasticine (modelling clay).
Attach a chain of paper clips to the pocket clip so that the pen top can float near the surface of water with the paper clips hanging down.
Almost fill a large plastic drink bottle with water.
Hold the pen top vertically over the bottle with the paper clips hanging down then gently lower it into the water.
Screw the drink bottle cap on tightly.
Squeeze the sides of the plastic drink bottle with your thumbs to make the pen top sink.
The pen top contains an air bubble.
When you squeeze the sides of the drink bottle, you also squeeze the air bubble, so more water enters the pen top and it sinks, because the air bubble displaces less water.
7. For a diver use a plastic sachet of sauce, mayonnaise or butter.
The type you see used in airlines.
The sachet contains some air.
When you put the sachet in a plastic bottle full of water and squeeze the bottle, some the air is compressed, the volume of the sachet decreases and it sinks.
8. Use a tall wide mouth container or a plastic drink bottle.
Wrap copper wire around the narrow part of the rubber bulb from a medicine dropper to make a rubber diver.
Fill the container with water.
Put enough water in the rubber diver so that it only just floats in the container of water.
Most of the rubber will be under water.
You can adjust how much the rubber diver floats by pinching the bulb to remove air.
Cover the container with a sheet of rubber or plastic sheet and tie it to the sides of the container.
If you press on the tight cover, the rubber diver will sink.
If you stop pressing on the tight cover, the rubber diver will rise.
Repeat the experiment using a very small glass tube of a medicine vial instead of the rubber bulb to make a glass diver.
Add a small amount of ink to the water so you can see the level of water in the glass diver.
Note that when the cover is pressed down, the pressure is transmitted through the water to decrease the volume of the air bubble in the glass diver, so the water level rises in the tube.
When the volume of the air bubble is too small to hold up the glass diver by displacement of water the glass diver will sink.
When you stop pressing on the cover, the decrease in pressure is transmitted to the air bubble that expands, so the water level in the glass diver decreases.
The increased volume of the air bubble in the glass diver displaces enough water to provide an upward force by displacement of water to allow the glass diver to float again.
9. Use a big bottle of water and an inverted open vial or small test-tube as a diver.
Slightly inflate a rubber balloon by lowing in it and attach it to the mouth of the bottle.
Squeeze the balloon and diver sinks.
10. Use a big plastic drink bottle as a submarine.
Pierce a hole in the cap and in the bottom of the drink bottle.
Push a plastic tube through the hole in the lid.
Fill the drink bottle with water and let it sink to the bottom of a big tub of water.
Blow into the plastic tube and the submarine rises to the surface.
11. Fill a plastic drink bottle with water.
Keep the lid.
Cut a drinking straw down to 7 cm.
Seal one end of the drink straw with a small piece of Plasticine and seal the other end with a bigger piece of Plasticine.
Place the drinking straw in the bottle so that it floats vertically close to the top.
Replace the lid on the bottle.
Squeeze the drink bottle and watch the drinking straw, i.e. the diver, sink to the bottom.
When you squeeze the bottle, you increase the pressure on the diver, slightly decreasing its volume and thus increasing its density, just enough to cause it to sink below the water.
10.4.3 Cold air is heavier than warm air, inverted paper bag balance
See diagram 37.118: Balanced flasks
1. Use two identical paper bags that are the same size.
Inflate each bag by blowing into them as if they are balloons.
Tie the openings closed tightly with string.
Tie the end of the string into a loop and suspend the bags from the end of a balanced rod.
Move the loops along the rod until the inflated bags are exactly balanced.
Gently heat the air beneath one of the bags with a small candle.
The bag containing the heated air moves up and the bag containing the cooler air moves down.
Move the candle to under the other bag to see the same result.
[Comment: The bags are sealed and so the mass of gas is unchanged when heating or cooling takes place.
This experiment shows Archimedes Principle in action, not mass change.]
2. Open two same size paper bags.
Attach identical pieces of string to the bottom of each bag with an identical pieces of adhesive tape.
Make a loop in the other end of each piece of string.
Put the loops over each end of a balanced rod.
Adjust the positions of the loops until the rod is horizontal.
Heat the air below one paper bag.
The end of the rod supporting that paper bag rises.
Leave the balance to stand without heating a bag.
The rod becomes horizontal again.
Heat the air below the other bag.
The other end of the rod rises.
This experiment shows that a volume of warm air weighs slightly less than a volume of cool air.
However, the experiment does not give any information about the weight of a volume of air.
The flame under the paper bag heats the air in it and it expands, following Charles's law.
Some heated air spills out of the paper bag leaving less air and less dense air in the paper bag.
The air in the heated paper bag weighs less than the air it displaces so by Archimedes' principle there is an upthrust greater than its weight that causes the paper bag to rise.
When you remove the flame, the warm air in the paper bag cools and contracts drawing in air at atmospheric pressure.
The weight of a paper bag full of air and the bag crunched together, with all the air squeezed out, is the same.
Air in a hot air balloon is heated, it expands and becomes lighter and the balloon is pushed up, because the air left in the balloon is less dense than the surrounding atmospheric air.
10.4.4 Different siphons
1. Simple siphon
See diagram 12.4.0: Simple siphons
Use two tall glass bottles and fill each about half full of water.
Connect two 30 cm lengths of glass tube with a 30 cm rubber or plastic tubing.
Fill the tube with coloured water and pinch it.
Put a glass tube in each bottle of water.
Siphon the water back and forth by varying the height of the bottles.
2. Siphon replaces water for fish tank.
Use a one metre length of 10 millimetre diameter rubber hose.
Fill the hose with water then block both ends with fingers.
Put one end into water in a tank for goldfish then move away the finger the end under water.
Put another end into a bucket or basin on the floor below the end of the tube in the tank, then move away the finger from the end.
Water streams out of the tank towards the bucket or basin.
3. Make an U-tube siphon.
Use two beakers half full of water with a connecting U-tube full of water.
Lift one beaker then the other.
4. Make a siphon in a bell jar.
Transfer water through an U-tube from a sealed flask to an open beaker when the assembly is placed in a bell jar and evacuated.
5. Find pressure in a siphon.
Hook a manometer to the upper portion of a siphon.
6. Make a mechanical siphon from a siphon hung over a pulley to a lower level.
7. Use a gas siphon to transfer carbon dioxide from one beaker to another, intermittent siphon
10.4.5 Diving bell
See diagram 11.288: Model diving bell
1. Use a small wide mouth bottle with a two-holes stopper.
Put some stones or metal washers in the bottle so it floats in an upright position.
Insert one arm of a U-tube through the stopper so that it extends to the bottom of the bottle.
Insert a short length of glass tubing through the other hole and attach a long rubber tube.
Put the bottle in water.
Suck on the rubber tube.
Water enters the bottle through the U-tube until the bottle sinks.
You can make the bottle rise by blowing through the rubber tube.
This model illustrates the principle of the tanks or pontoons used to lift sunken ships.
Fasten a weight to the bottle, sink both in water and lift the weight by blowing air into the bottle.
2. Crumple newspaper and push it into the bottom of a drinking glass.
Invert the glass and check that the newspaper will not fall out of the glass.
Push the inverted glass down into a container of water.
Water rises slightly in the glass, but does not wet the newspaper fixed in the bottom of the glass.
A diver can swim into a diving bell and breath in some of the compressed air stored in it.
10.4.6 Mariotte bottle, (Mariotte flask, Mariotte siphon)
See diagram 12.4.1.1: Mariotte bottle
A Mariotte flask (Edme Mariotte, 1620-1684, France), gives a constant flow of water. because it gives a constant pressure of the output liquid independent of the input pressure / volume of the liquid.
It has an outlet tube near the bottom and an adjustable air inlet tube running out through the top.
If filled above the level of the bottom of the air inlet tube, it gives a flow of constant head of water equal to the height of the bottom of the bottom air inlet tube above the outlet.
The pressure at the bottom of the air inlet tube is always at atmospheric pressure.
A head of water is water kept at a height to provide a supply, referring to its height or the pressure it exerts, so a Mariotte bottle is called a constant head device.
Mariotte bottles have been used to study the transition from laminar to turbulent flow with different shaped outlets.
Experiments
1. Cut a hole in the side of a 2-litre plastic drink bottle, 2 cm above the base, wide enough for a flexible outlet tube to fit through it.
Use glue to seal between the drink bottle wall and flexible outlet tube.
2. Drill a hole in the cap of the bottle, or use a 1-hole rubber or cork stopper, with the hole wide enough for a plastic air inlet tube to fit through it.
Apply grease between the air inlet tube and cap or stopper to allow the air inlet tube to be moved up or down.
3. Clamp the flexible outlet tube, add water to the bottle to about the 3/4 level, and attach the cap or stopper with the air inlet tube.
4. Adjust the position the bottom of the air inlet tube to level 1 in the diagram and unclamp the outlet tube.
The inlet tube is full of air with a bubble at its lower end, but no bubbles emerge to pass up through the water.
No water passes through the outlet tube, because the pressure at the bottom of the air inlet tube is atmospheric pressure as is the pressure outside the outlet tube.
5. Move the lower end of the inlet tube to level 2.
Water flows out through the outlet tube and bubbles from the end of the inlet tube pass up through the water.
Measure the flow rate of water through the outlet tube with a graduated cylinder and a stop watch.
Observe the shape of the jet of water exiting the outlet tube.
The pressure at the bottom of the air inlet tube is still atmospheric pressure.
However, at the entrance to the outlet tube the pressure is a combined pressure of atmospheric pressure + the pressure at the base of the column of water between level 1 and level 2.
6. Clamp the outlet tube and move the lower end of the inlet tube to level 3.
Measure the flow rate of water through the outlet tube with a graduated cylinder and a stop watch.
The flow rates at level 2 and level 3 are the same.
Observe the shape of the jet of water exiting the outlet tube.
As long as the water surface is above the level 1, the water jet should have the same profile.
7. Raise the end of the flexible outlet tube above the level end of the air inlet tube, but below the level of the water surface in the bottle.
The flow of water through the flexible outlet tube stops even though it is below the water surface in the bottle.
8. Remove the air intake tube.
The water in Mariotte flask now behaves like the water in a bucket.
The flow rate at the exit will depend upon the level of the water surface, and the shape of the outlet jet will change as the water surface drops.
The flow of water through the outlet tube continues until the end of the outlet tube is raised above the level of the water surface in the bottle.
10.4.7 Plastic syringes and air pressure
See diagram 12.301: Syringes and air pressure
Vacuum Stoppers, creates near vacuum in plastic syringe (industrial product)
[Some school systems do not allow the use of syringes in the classroom.]
1. With the tip sealed, use a syringe to compress air or to produce a partial vacuum.
Attach a small piece of plastic tubing to let you seal the tip with a pinch clamp or seal the syringe by pushing the tip into a wooden block drilled to the appropriate size.
With this base as a platform, use the syringe in a vertical position as a balance for measuring weight by air compression.
You can quantify all the following experiments, because syringes are already graduated.
2. Fill the syringe with a small amount of air and hang it inverted to serve as a "spring type" balance.
3. Compress moist air within a syringe to cause water condensation and make "artificial rain".
4. Attach a length piece of plastic tubing to make a simple syringe pump.
5. Put water in the tube to make an air thermometer or use 12 m of tubing to make a water barometer.
6. Couple two syringes with a piece of tubing to show pressure changes within closed systems.
10.4.8 Self-starting siphon, self-siphoning beads / gel
See diagram 12.4.4: Self-starting siphon
1. When the loop is submerged the siphon starts flowing.
When point 1 is submerged water rushed through the tube towards point 2.
Then carries over past point 2 towards point 3, because of its inertia.
After passing point 3, the water moves down the tube by gravitational attraction, pulling water to follow behind it at point 3 by the forces of cohesion.
This kind of siphon can be made with "bendy" drinking straws.
2. Self-siphoning beads
"Newtons Flying Beads". (product to amuse children)
The beads are balls linked by straight connectors so when the end of the bead chain is pulled over the lip of the container it stars to fall pulling the beads in the contained behind it.
The connections between the beads do not allow a sharp fold over the edge of the container so the bead chain arches up to form a loop.
3. Self-siphoning gel
"Poly-Ox", polyethylene oxide, non-Newtonian self siphoning gel, (product to amuse children)
The gel contains molecule of very high molecular weight so that when the gel is first poured the gel past the rim of the contains falls down and pulls up and over the rim the gel behind it.
10.4.9 Siphon fountain
See diagram 12.4.1: Siphon fountain
1. Fit a glass container, or a flask made from a used electric bulb with a two-holes rubber stopper.
Through one hole place a jet tube which will extend to about half way to the top of the flask and about 2 cm outside the stopper.
Through the other hole push a short length of glass tube so that it is just flush with the bottom of the stopper.
Connect a 20 cm length of rubber tube to the jet tube.
Connect a 1 m length to the other glass tube.
Place some water in the flask and insert the stopper.
Put the short rubber tube in a container of water on a table, let the longer rubber tube go into a bucket on the floor and then invert the siphon.
Add ink to the water to see the fountain better.
Make a double siphon fountain by making another flask unit similar to the first one and connect them.
2. Insert 2 pieces of glass tubing through a 2-hole stopper such that one extends farther than the other.
Connect 30 cm of rubber tubing to each glass tube.
Fill a large bottle with cold water.
Pour 100 mL of water in a large jar and insert the 2-hole stopper with attached tubing.
Invert the jar.
The ends of the tubing in the bottle should be under water at all times.
Observe what happened after inverting the jar.
Observe the volume of the air pocket above the water in jar as the water poured in the empty bottle.
Note that water was drawn up into the jar.
The bottle filled with water had to stand higher than the other bottle.
See how to make the fountain flow more or less.
The water in the jar was needed to "prime" the siphoning action.
After inverting the jar, the water ran down and into the empty bottle causing an increase in volume of the air pocket above the water in the jar and decreasing the pressure.
The lower pressure caused the sucking up of the water from the bottle filled with water.
The atmospheric pressure pushes water up into the larger jar.
The greater the difference in height of the water levels in the two jars, the greater the flow of water.
As soon as the water levels are the same height in both bottles the water flow stops as in a siphon.
3. Fit a glass container, or a flask made from a used electric bulb with a 2-hole rubber stopper.
Through one hole place a jet tube that extends to about half way to the top of the flask and about 2 cm outside the stopper.
Through the other hole push a short length of glass tube so that it is just flush with the bottom of the stopper.
Connect a 20 cm length of rubber tube to the jet tube.
Connect a 1 m length to the other glass tube.
Place some water in the flask and insert the stopper.
Put the short rubber tube in a container of water on a table.
Let the longer rubber tube go into a bucket on the floor and then invert the siphon.
Add ink to the water to see the fountain better.
Make a double siphon fountain by making another flask unit si
10.4.10 Turnover siphon
See diagram 12.4.10: Turnover siphon
1. Insert two pieces of glass tubing through a 2-hole stopper with a longer piece drawn out to form a jet.
Connect the shorter glass tube with rubber tubing to a lower jar, A.
Connect the longer glass tube with rubber tubing to a higher jar, B.
Add water to an elevated jar, C.
Insert the 2-hole stopper in C so that the jet end of the longer glass tube is above the water level.
Fill jar B with water.
2. Invert jar C while keeping the ends of the rubber tubes in the jars.
Water in jar C starts to run down the rubber tube into jar A, increasing the volume of air in jar C, and decreasing the air pressure in jar C.
Water in jar B is pushed up the rubber tube by (atmospheric pressure - air pressure) in jar C.
The water shoots out through the jet end of the longer glass tube until the levels of water in jar B and jar C are the same.
10.4.11 Flask fountain
Boil some water in a flask and insert a one hole stopper with a single tube then invert the apparatus with the lower end of the tube under water in a beaker.
At first water moves slowly up the tube, but as water touches the inside of the flask cooling quickens and water moves more quickly up the tube.
Make the colour of the water change by putting dilute hydrochloric acid in the in the flask and bromothymol blue in the beaker.
10.6.0 Archimedes
10.6.1 Archimedes' principle
10.6.2 Archimedes' bucket and cylinder experiment
10.6.3 Archimedes' burning ship
10.6.4 Archimedes' screw
10.6.5 Archimedes and the gold crown of King Hiero
10.6.1 Archimedes' principle
Archimedes of Syracuse, about 287-212 BC
"His work "On Floating Bodies", is generally considered to be the first major work on Fluid Mechanics." (Wikipedia).
See diagram 11.4.0: Archimedes' principle
See diagram 11.4.8: Archimedes' principle experiment
See diagram 11.200.1: Archimedes' principle
See diagram 11.4.9: Bucket and cylinder experiment
See diagram 11.4 0.1: Archimedes' principle
See diagram 12.4.1.0: Difference in heights of water columns
See diagram 12.4.05: Siphon systems showing pressure each side of fluid disc, Syringe
Archimedes' principle:
A body immersed in a fluid is subject to an upward force equal in magnitude to the weight of fluid it displaces.
A body wholly or partly immersed in a fluid is subject to a buoyancy force of magnitude equal to that of the weight of the displaced fluid.
The upthrust or buoyancy force on an object, wholly or partially immersed in a fluid, is equal in magnitude and opposite to the weight of the fluid it has displaced.
The apparent loss in weight of a body immersed in a liquid will equal the weight of the displaced liquid.
Buoyancy force = (force on top surface of object - force on bottom surface of object) = (F2 - F1).
= (P1A - P2A).
= (density × gh1A - density × gh2A).
= density × gA (h2 - h1.
= weight of displaced fluid.
Experiment
1. Fill an overflow can.
2. Put a wooden block in the overflow can.
3. Collect the water displaced in a balance pan.
4. Remove the wooden block, dry it, put it in the other balance pan.
The weight of the wooden block is equal to the weight of the water displaced.
The apparent loss in weight of a body immersed in a liquid will equal the weight of the displaced liquid.
Buoyancy force = (force on top surface of object - force on bottom surface of object) = (F2 - F1)
= (P1A - P2A) = (density × gh1A - density × gh2A)
= density × gA (h2 - h1) = weight of displaced fluid.
The upthrust or buoyancy force on an object wholly or partially immersed in a fluid is equal in magnitude and opposite to the weight of the fluid it has displaced.
10.6.2 Archimedes' bucket and cylinder experiment
Buckets, bucket and rod, bucket and cylinder, (Commercial)
See diagram 11.4.9: Bucket and cylinder experiment
The all-metal bucket and cylinder demonstrates the principles of buoyancy and displacement.
The cylinder fits into the cup exactly.
The whole unit can be hung from a spring scale and weighed.
This unit can then be lowered into a container of water and the reduction weight noted.
The weight loss equals the weight of the water displaced.
Experiments
1. A solid metal cylinder C just fits into a cylindrical bucket B.
They are suspended from a balance arm, with the cylinder attached to a hook on the base of the bucket.
Add weights to the other balance pan until the balance arm is horizontal.
Immerse the solid cylinder in water by raising beaker A.
The buoyancy force on the immersed cylinder disturbs the equilibrium of the balance.
Upon filling the bucket with water balance is restored by the balance arm.
2. A mass and bucket of the same volume hang from a spring scale.
Lower the mass into water catch the overflow and pour the overflow into the bucket.
Hang a cylinder and bucket of the same volume from a scale.
Immerse the cylinder in water, catch the overflow and pour it into the bucket.
Hang a cylinder turned to fit closely inside a bucket from the bottom of the bucket while suspended from the bottom of a balance.
Immerse the cylinder in water and then pour water into the bucket.
Archimedes did not experience buoyancy, only how to measure volume.
3. A cylindrical mass and bucket are suspended from a spring scale above a beaker with an overflow spout.
Note the scale reading.
Submerge the mass by raising the beaker with the lab jack.
Pour the water from the catch bucket into the hanging bucket to return to the original scale reading.
You may also show that the mass exactly fits inside the hanging bucket.
Note the reading of the spring scale suspending a cylindrical mass and hanging bucket above an overflow beaker.
The cylindrical mass fits exactly into the catch bucket.
Raise the overflow beaker to submerge the mass and bucket and let the displaced water flow into a catch beaker.
Lower the overflow beaker and remove the cylindrical mass from the bucket.
Dry the hanging bucket then pour the water from the catch beaker into the catch bucket.
The reading on the spring scale is the same as at the start of the experiment.
10.6.3 Archimedes' burning ship
Show the concentration of light energy by using of multiple mirrors.
Use a light dependant oscillator, 0-100 A4 Mirrors (Mylar on Cardboard), a concave Mirror and a 1500W flood light.
Archimedes is supposed to have destroyed a naval attack by having his soldiers reflect the suns rays from polished shields onto the sails of an enemy fleet.
In this re-enactment, distribute mylar mounted on A4 cardboard amongst the student audience.
The mirrors reflect the light from a 1500W floodlight onto an electronic oscillator whose frequency is light dependent.
This demonstration was attempted by the "Mythbusters" program, at the request of President Obama, but they declared the myth ""busted", because the large scale array manipulated by hundreds of volunteers simply took too long to light the ship on fire.
The ship ignited only when it was stationary and positioned at less than half the distance described in the myth.
However, the myth was plausible at a smaller scale.
In 1973, a Greek scientist, Dr Ioannis Sakkas, curious about whether Archimedes could really have used a burning glass to destroy the Roman fleet
in 212 BC lined up nearly 60 Greek sailors, each holding an oblong mirror tipped to catch the Suns rays and direct them at a wooden ship 160 feet away.
The ship caught fire at once.
Dr Sakkas said after the experiment there was no doubt in his mind that the great inventor Archimedes could have used bronze mirrors to scuttle the Romans.
10.6.4 Archimedes' screw
See diagram 21.3.02: Archimedes' screw is a hollow inclined screw so that rotation of the screw raises water.
It was invented by Archimedes, but apparently was not invented in China.
10.6.5 Archimedes and the gold crown of King Hiero
(Archimedes of Syracuse, about 287-212 BC)
Marcus Vitruvius Pollio (85 BC - 20 BC) wrote a 10 volume work "On architecture", which included the following account of Archimedes and the gold crown of King Hiero some 200 years after the event:
"DE ARCHITECTURA LIBRI DECEM, by Marcus Vitruvius Pollio
BOOK IX, INTRODUCTION
"9. In the case of Archimedes, although he made many wonderful discoveries of diverse kinds, yet of them all, the following, which I shall relate, seems to have been the result of a boundless ingenuity.
Hiero, after gaining the royal power in Syracuse, resolved, as a consequence of his successful exploits, to place in a certain temple a golden crown, which he had vowed to the immortal gods.
He contracted for its making at a fixed price, and weighed out a precise amount of gold to the contractor.
At the appointed time, the latter delivered to the king's satisfaction an exquisitely finished piece of handiwork, and it appeared that in weight the crown corresponded precisely to what the gold had weighed.
10. But afterwards a charge was made that gold had been abstracted and an equivalent weight of silver had been added in the manufacture of the crown.
Hiero, thinking it an outrage that he had been tricked, and yet not knowing how to detect the theft, requested Archimedes to consider the matter.
The latter, while the case was still on his mind, happened to go to the bath, and on getting into a tub observed that the more his body sank into it the more water ran out over the tub.
As this pointed out the way to explain the case in question, he jumped out of the tub and rushed home naked, crying with a loud voice that he had found what he was seeking; for he as he ran he shouted repeatedly in Greek, Εὕρηκα, εὕρηκα [= Eureka, eureka = I have found (it), I have found (it)].
11. Taking this as the beginning of his discovery, it is said that he made two masses of the same weight as the crown, one of gold and the other of silver.
After making them he filled a large vessel with water to the very brim, and dropped the mass of silver into it.
As much water ran out as was equal in bulk to that of the silver sunk in the vessel.
Then, taking out the mass, he poured back the lost quantity of water, using a pint measure, until it was level with the brim as it had been before.
Thus he found the weight of silver corresponding to a definite quantity of water.
12. After this experiment, he likewise dropped the mass of gold into the full vessel and, on taking it out and measuring as before, found that not so much water was lost, but a smaller quantity: namely, as much less as a mass of gold lacks in bulk compared to a mass of silver of the same weight.
Finally, filling the vessel again and dropping the crown itself into the same quantity of water, he found that more water ran over the crown than for the mass of gold of the same weight.
Hence, reasoning from the fact that more water was lost in the case of the crown than in that of the mass, he detected the mixing of silver with the gold, and made the theft of the contractor perfectly clear."