204 Simple Science Experiments ~ {ERG} - Page 7

LoneRanger · #91 07-04-2008, 01:14 PM

79. Expanded air

Pull a balloon over the mouth of a bottle and place in a saucepan of cold water. If you heat the water on a stove, the balloon is seen to fill with air. The air particles in the bottle whirl around in all directions, thus moving further apart, and the air expands.

This causes an increased pressure, which escapes into the balloon and causes it to distend. If you take the bottle out of the saucepan, the air gradually cools down again and the balloon collapses.

LoneRanger · #92 07-05-2008, 12:49 PM

80. Buddel thermometer

Pour some coloured water into a bottle. Push a drinking straw through a hole bored in the cork so that it dips into the water. Seal the cork with glue. If you place your hands firmly on the bottle, the water rises up the straw.

The air enclosed in the bottle expands on heating and presses on the water surface. The displaced water escapes into the straw and shows the degree of heating by its position. You can fix a scale on the side of the bottle.

LoneRanger · #93 07-06-2008, 02:37 PM

81. Hot-air balloon

Roll a paper napkin into a tube and twist up the top. Stand it upright and light the tip. While the lower part is still burning, the ash formed rises into the air. Take care!

The air enclosed by the paper is heated by the flame and expands. The light balloon-like ash residue experiences surprising buoyancy because the hot air can escape, and the air remaining in the balloon becomes correspondingly lighter. Very fine napkins are not suitable for the experiment because the ash formed is not firm enough.

LoneRanger · #94 07-07-2008, 04:39 PM

82. Expanding Metal

Take an empty, corked wine bottle, push as long an aluminum knitting needle as you can find into the bottle cork and let the other end project under slight pressure over the mouth of a second, uncorked bottle. Glue a paper arrow on to a sewing needle, making sure that it is balanced, and fix it between the knitting needle and the neck of the bottle. Place a candle so that the tip of the flame touches the middle of the needle and watch the arrow.

The arrow turns quite quickly some way to the right because the knitting needle expands on heating like other substances. With an ordinary steel knitting needle the arrow would only turn a little, because steel only expands half as much as aluminum. Since the aluminum is longer as well, the difference is still greater. The expansion is clearly visible in electricity power cables, which sag more in summer than in winter. If you take the candle away from the knitting needle, the arrow moves back.

LoneRanger · #95 07-09-2008, 01:32 PM

83. Exploding stone

You can explode large stones in the winter quite easily.

Look for a flint that is well frozen through and pour boiling water over it. It breaks apart with cracks and bangs. The explosive effect is caused by the outer layers heating and expanding faster than the centre. The resulting tension causes the stone to burst. In the same way thick-walled glasses may explode if you pour hot liquids into them. Glass conducts heat poorly, so that the layers of glass expand by different amounts.

LoneRanger · #96 07-10-2008, 12:50 PM

84. A clear case

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Put spoons made of steel, silver, and plastic and a glass rod into a glass. Fix a dry pea at the same height on each handle with a dab of butter. In which order will the peas fall if you pour boiling water into the glass?
The butter on the silver spoon melts very quickly and releases its pea first. The peas from the steel spoon and the glass rod fall later, while that on the plastic spoon does not move. Silver is by far the best conductor of heat, while plastic is a very poor conductor, which is why saucepans, for example, often have plastic handles.

LoneRanger · #97 07-11-2008, 01:01 PM

85. Non-Inflammable Material.

Place a coin under a cotton handkerchief and ask someone to press a burning cigarette on the cloth stretched over the coin. You need not be afraid of scorching the material, because only a harmless speck of ash will be left.

The experiment shows that the metal of the coin is a much better conductor of heat than the cotton fabric. On rapid pressure the heat of the burning cigarette is immediately conducted away by the coin. There is only enough heat to cause a small rise in temperature in the coin, and the cotton does not reach a high enough temperature to burn.

LoneRanger · #98 07-12-2008, 01:35 PM

86. Fireguard

Hold a metal kitchen sieve in a candle flame. To your surprise the flame only reaches the wire net, but does not go through it.

The metal in the sieve conducts so much heat away that the candle wax vapor cannot ignite above the wire net.

The flame only passes through the metal lattice if it is made to glow by strong heating. The miner’s safety lamp works in the same way. A metal lattice surrounding the naked flame takes up so much heat that the gases in the mine cannot ignite.

LoneRanger · #99 07-13-2008, 01:57 PM

87. Scenting coins

Three different coins lie in a plastic dish. You close your eyes while another person takes out one
coin, holds it for several seconds in his closed hand, and puts it back. Now hold the coins one after
the other briefly to your upper lip and find out immediately, to everyone’s astonishment, which coin
was taken from the dish. Since metals are very good conductors of heat, the coin warms up immediately
in the hand. But plastic is a poor conductor, so hardly any heat is lost to the dish when the coin is put
back. The upper lip is particularly sensitive and reveals the smallest temperature difference in the
coins, so that you can detect the right one immediately. Before the trick is repeated it is a good idea
to lay the coins on a cold stone floor to conduct away the heat.

LoneRanger · #**100** 07-14-2008, 02:01 PM

88. Fire Under Water

Warm the base of a candle stump and stick it in a bowl. Fill the bowl with cold water up to the rim of the candle. If you light the wick it burns until it is under the surface of the water. Then the candle flame hollows out a deep funnel. An extremely thin wail of wax remains standing round the flame and stops the water from extinguishing it. The water takes so much heat from the candle that its outer layer does not reach its melting
point, and the wax there cannot evaporate and burn.

LoneRanger · #**101** 07-15-2008, 01:55 PM

89. Paper saucepan

Do you believe that you can boil water in a paper cup over a naked flame or in the embers of a fire!

Push a knitting needle through the rim of a paper cup containing some water, hang it between two upright bottles and light a candle under the cup.

After a little while the water boils - but the cup is not even scorched.

The water removes the heat transferred to the paper and begins to boil at a temperature of 212F or 100C.

The water does not get any hotter, so the paper does not reach the temperature, which is necessary for it to burn.

LoneRanger · #**102** 07-16-2008, 08:59 PM

90. Jet boat

Bore a hole from the inside through the screw top of an aluminium pill tube about four inches long, and pour some water into the tube. Fix the tube in an empty sardine can into which you have fixed three candle stumps and place the can in water. If you light the candles the water soon boils, and the jet of steam escaping from the back drives the boat.

Steam is formed in the boat’s boiler when the water boils. Because it expands sharply, it escapes at high pressure through the nozzle and causes a recoil. Do the experiment in calm weather!

LoneRanger · #**103** 07-17-2008, 01:14 PM

91. Hovercraft

Place a tin lid on a hot plate and heat it well (take care!). If you then let a few drops of water fall on the lid, you will observe a small natural phenomenon. The drops are suspended in the air like hovercraft and whiz hissing to-and-fro for a while.

On contact with the heated metal the water drops begin to evaporate at once on the underside. Since the steam escapes with great pressure, it lifts the drops into the air. So much heat is removed from the drops by the formation of steam that they do not even boil.

LoneRanger · #**104** 07-18-2008, 02:37 PM

92. Rain In The Room

Rain after sultry days makes the inside of the windowpane suddenly sweat. You can distinguish the tiny water droplets through a magnifying glass. Where do they come from?

After it has been raining the air outside cools sharply because the water evaporates and thus uses heat. The warm air in the room, which is saturated with water vapor, especially from cooking, cools down only slowly on the windowpane. But cold air cannot hold so much moisture as warm air, and therefore loses some of it on to the pane. It forms water droplets - exactly as when it is raining out-of- doors and moist, warm air meets cold air.

LoneRanger · #**105** 07-19-2008, 12:39 PM

93. Weather station

Fix a dry pinecone on to a small piece of wood with sealing wax or glue. Stick a pin into one of the central scales and place a straw over it. Put the cone out-of- doors, protected from the rain. The straw moves according to the state of the weather. Fix up a scale.

This simple hygrometer was built by nature. The pinecone closes when it is going to rain, to protect the seeds from damp. The outside of the scales absorbs the moisture in the air, swells up and bends - a process which you can also observe with a piece of paper which is wet on one side.