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Build six dice made of ivory or plastic into a tower and place a coin in the middle, using a quarter-dollar or a 5 new-penny piece. The tower is very rickety: then how can you remove the coin without touching it or knocking it over?

Hold a ballpoint pen with a pushing device a little way from the coin. If you discharge it the coin flies out of the tower.

The movement of the spiral spring in the ballpoint pen is transferred at once to the coin, but because of the low friction not to the dice, which because of their weight have a fairly large inertia

Lay a small board on a glass of water, place on it a matchbox case, and on this a raw egg. Can you transfer the egg to the water without touching it? Pull the board
sharply to the side! The egg falls undamaged into the water.

Inertia of the egg is so great because of its weight that it is not carried along with the fast movement. The light box, on the other hand, flies off because its inertia is low.

Tie two pieces of cord of equal thickness to a block of wood or another heavy object. Hang the wood up by one cord and pull on the other. Which section of cord will break?

If you pull slowly, the strain and the additional weight of the object causes the upper cord to break. (Please be careful that the object does not fall on your hand).But if you pull jerkily, the inertia of the block prevents the transfer of the total force to the upper cord, and the lower one breaks.

Cut far enough into the flesh of an apple with a knife, so that when you lift it up it sticks to the blade. Now knock against the blade in the apple with the back of another knife. After several blows the apple will break in half.

The famous Italian scientist Galileo discovered in the sixteenth century that all bodies offer a resistance to an alteration in their position or state of motion, which we call inertia. This prevents the apple from following the jerky movements of the knife. It pushes slowly on the blade, until it is separated.

Place about 20 coins of the same value in a pile on a smooth table. How can you take away the coins one at a time from below, without touching them? Flip another coin sharply with your finger so that it hits the bottom coin and shoots it away.

If you aim well, you can shoot away all the coins in this way. The inertia of the coin column is so great that the force of the flipped coin is not sufficient to move it or completely overturn it.

A square piece of paper has one corner snipped off, and two notches made in the opposite corner. Roll the paper in the direction of the arrow in the figure to make a tube about as thick as a pencil and push the notched corner back into the opening.

Draw a deep breath through the tube. This causes a loud humming note. The air, which is drawn in sucks up the paper corner, but since it is slightly springy, it begins to vibrate. The vibration is quite slow, so the note is deep.

Cut a piece about an inch long from a plastic drinking straw. Press one end together and cut it to a point. If you fix the straw against the front of the top palate, you can obtain various notes when you blow through it. The pointed tongues of the straw are moved in very rapid sequence by the air sweeping through, so that the note produced is fairly high. A large number of musical instruments are based on this simple principle.

Half fill a thin walled glass with water, dip in your forefinger and run it slowly round the rim of the glass. A lovely, continuous ringing note is produced.

The experiment only works if your finger has just been washed. It rubs over the glass, giving it tiny jolts. The glass begins to vibrate, which produces the note. If your finger is greasy, it slides smoothly over the glass without the necessary friction.

The pitch of the note depends on the amount of water, and the vibration can be seen clearly on the water surface.

You can extend the previous experiment. Place two similar thin walled glasses an inch apart and pass your freshly washed finger slowly round the rim of one of them. A loud humming note is produced. In a strange way the second glass vibrates
with the first, and you can observe this vibration if you place a thin wire on it.

The vibration of the first glass is transmitted to the second by the sound waves in the air. This ‘resonance’ only occurs if the glasses produce notes of the same pitch when struck. If this is not the case with your two glasses, you must pour some water into one until the pitches are the same.

Tie a fork in the middle of a piece of string about a yard long. Wind the ends several times round your forefingers and hold the tips of your fingers in your ears. Let the fork strike a hard object. If the string is then stretched, you will hear a loud, bell-like peal.

The metal vibrates like a tuning fork when it strikes the hard object. The vibration is not carried through the air in this case, but through the string, and the finger conducts it directly to the eardrum.

Halve a match, make a point on it and split it at the other end. Fix it on to a smooth piece of paper and hold it vertical on an old turning phonograph record. The music sounds over the paper almost as clearly as from a loudspeaker.

The match travels in the grooves of the record and transfers the lateral vibrations to the paper like a phonograph needle to the diaphragm of a loudspeaker. The vibrations of the paper are carried to your eardrum as sound waves through the air.

Nail as large a tin can as possible firmly onto a suitable board A. Through board B, which is fixed at the side, bore a hole through which you can turn an iron screw C to the middle of the base of the tin.

A small space should remain between screw and tin. Put a layer of paper E round the screw and over it wind about two yards of covered wire F. From the inside a wood screw K, which is fixed so it can be moved in a piece of wood H, contacts the base of the tin. Scrape off the metal plating in front of the tip of the screw and oil it. Join all the parts correctly with connecting wire, removing the insulation and tin varnish from the-connecting points. A clothes peg with two drawing pins M and N acts as the horn button.

If you press it, you will obtain a very loud signal. The apparatus works on the same principle as a car horn. If you close the circuit by pressing the horn button, the screw C becomes magnetic and attracts the base of the tin. So the circuit is broken in front of the screw K. Screw C loses its magnetism, and the base of the tin springs back to the screw K. The process is repeated so quickly that the tin plate produces the horn note by its vibration.

Put a house fly in a smooth paper bag, close it, and hold it horizontally above your ear. If you are in a quiet room you can hear the patter of the six legs and other rather curious noises quite clearly.

The paper behaves like the skin of a drum. Although only the tiny legs of the insect beat on it, it begins to vibrate and transmits such a loud noise that you would imagine that a larger organism or a rattling clockwork motor was in the bag.