204 Simple Science Experiments ~ {ERG}

[LoneRanger]

117. Sloping path

If you cool a boiled egg in the usual way under the water tap, you can make a surprising discovery. Hold the
saucepan so that the water runs between the egg and the rim. If you now lean the saucepan to the other side the egg does not, as you would expect, roll down the bottom of the saucepan, but stays in the stream of water.

By Bernouilli’s Law the pressure of a liquid or a gas becomes lower with increasing speed (see experiments 69 - 74). In the stream of water between the rim of the pan and the egg there is reduced pressure, and the egg is pressed by the surrounding water, which is at normal pressure, against the pan.

[LoneRanger]

118. Loss of weight

Tie a stone by means of a thread to a spring balance and note its weight. Does it in fact alter if you hang the stone in a jar of water! If you lift up a large stone under the water when you are bathing you will be surprised at first by its apparently low weight. But if you lift it out of the water, you will see how heavy it actually is. In fact an object immersed in a liquid (or in a gas) loses weight.

This is particularly obvious with a floating object. Look at the experiment tomorrow.

[LoneRanger]

119. Archimedes’ principle

Fill a container up to the brim with water and weigh it. Then place a block of wood on the water, and some of the liquid will spill out. Weigh again, to find out if the weight has altered.

The weight remains the same. The water spilt out of the container weighs exactly the same as the whole block of wood. The famous mathematician Archimedes discovered in about 250 BC that a body immersed in a liquid loses as much weight as the weight of liquid displaced by it. This apparent loss of weight is called buoyancy.

[LoneRanger]

120. Water puzzle

Lay a small tray or a wooden ruler over a six-sided pencil and place on it two jars filled with water balanced as on a pair of scales. What happens if you immerse a cork into the water in one jar, while placing a cork of the same size on the water in the other jar! Does one side of the balance become heavier, and if so, which side!

The balance leans to the side where you immerse the cork in the jar. That is, this side increases in weight by exactly as much as the weight of water displaced by the cork. The other jar only becomes as much heavier as the weight of the cork itself.

[LoneRanger]

121. Mysterious water level

Place a half-dollar, ten new pence, or a penny in a matchbox and float it in a glass of water. Mark the level of the water on the side of the glass. Will it rise or fall if you take the coin from the box and lower it into the water! Just think about it first!

The water level falls. Since the coin is almost ten times heavier than water, the box containing the coin also displaces, because of its larger volume, ten times more water than the coin alone. This takes up, in spite of its greater weight, only a small volume and so displaces only a small amount of water.

[LoneRanger]

122. Volcano under water

Fill a small bottle full of hot water and colour it with ink. Lower the bottle by means of a string into a preserving jar containing cold water. A coloured cloud, which spreads to the surface of the water, rises upward out of the small bottle like a volcano.

Hot water occupies a greater volume than cold because the space between the water particles is increased on heating. It is, therefore, lighter and experiences buoyancy. After some time the warm and cold water mix and the ink is evenly distributed.

[LoneRanger]

123. Suspending an egg

Half fill a jar with water and dissolve plenty of salt in it. Now add as much water again, pouring carefully over a spoon so that the two liquids do not mix. An egg placed in the jar remains suspended as though bewitched in the middle. Since the egg is heavier than tap water, but lighter than salt water, it sinks only to the middle of the jar and floats on the salt water. You can use a raw potato instead of the egg. Cut a roundish ‘magic fish’ from it, and make fins and eyes from colored cellophane.

[LoneRanger]

124. Dance of the mothballs

Add some vinegar and bicarbonate of soda to some water in a jar. Toss several mothballs, which you can colour beforehand with a crayon to make the experiment more fun, into the bubbling bath’. After a time the balls dance merrily up and down. Since the mothballs are a little heavier than water, they sink to the bottom of the jar. The carbon dioxide freed by the chemical reaction between vinegar and bicarbonate of soda collects in bubbles on the balls and lifts them slowly to the surface of the water. There the bubbles escape the balls sink again, and the performance is repeated.

[LoneRanger]

125. Pearl diver

Stick a match about one-tenth of an inch deep into a coloured plastic bead and shorten it so that its end floats exactly on the surface of the water when the bead is placed in a milk bottle full of water. Close this with a plastic cap.

By changing the pressure on the cap, the bead can be made to rise and fall as though bewitched. Plastic is only a little heavier than water. The match and the air in the hole of the bead give it just enough buoyancy for it to float. The pressure of the finger is conducted through the water and compresses the air in the bead. Thus it no longer has sufficient buoyancy and sinks.

[LoneRanger]

126. The yellow submarine

Cut a small boat out of fresh orange peel and make portholes on it with a ballpoint pen. Place the boat in a bottle filled with water and close it with a plastic cap, if you press on the cap, the boat rises and falls according to the strength of the pressure. Minute air bubbles in the porous fruit peel make it float. By the pressure of the finger, which is transmitted through the water, the bubbles are slightly compressed, so their buoyancy is less, and the boat goes to diving stations. Since the yellow of the peel is heavier than the white, the submarine floats horizontally.

You can accompany the submarine by several ‘frogmen’. Simply toss broken-off match heads with it into the bottle. They float, because air is also contained in their porous structure. If the air bubbles are made smaller by the transmitted water pressure, the match heads dive deeper too.

[LoneRanger]

127. Bewitched box

Stick a false bottom in a thin cardboard box and hide a lead weight in the space below. You can always balance the box on the corner in which the piece of lead is lying. Each object has a centre of gravity, round which it is held in balance by the force of gravity. In such a regularly shaped object as a box the centre of gravity is exactly in the middle, so your box should fall from the table. The lead weight prevents this, however, by shifting the centre of gravity above the table.

[LoneRanger]

128. The balancing button

If you place a button on a cup so that only the edges are in contact, it will fall off at once. No-one would think that the button would remain on the rim of the cup if you fixed yet another weight on to it. And yet it is possible. If you fix two kitchen forks over the button and then place it on the rim of the cup, it will remain in this position.

The bent fork handles, whose ends are particularly heavy and reach sideways round the cup, move the center of gravity of the button exactly over the rim of the cup, so that the whole set-up is in balance

[LoneRanger]

129. Floating beam

It would not seem possible to balance a clothes peg with one end on the tip of your finger if a leather belt is hung over half the peg. But the force of gravity can apparently be overcome. The whole secret is a small nick, which you cut slantwise in the
piece of wood. The belt, which you squeeze firmly into the nick, leans so far sideways because of its slanting fixing that the center of gravity of wood and belt together is shifted under the tip of the finger and balance is obtained.