On the neck of a bottle place a cork in an upright position. The cork must be large enough to rest on the neck without falling in.

Now give a sharp fillip on the neck of the bottle, and you will see the cork fall, not on the other side of the bottle as most people expect, but forward in the direction of the hand giving the blow. This, again, is an illustration of the principle of inertia. A rapid blow tends to push the bottle from the cork before the movement is transmitted to the latter.

Few people will execute this experiment properly the first time, for the instinctive fear to break the bottle and cut their fingers, will prevent them giving a blow sharp enough to make this experiment successfully at the first attempt; but with a little perseverance, the necessary degree of force will be gauged to a nicety.