The Refractory Cork
A very interesting and amusing experiment may be performed with a bottle and a cork.
Take a cork of a diameter less than the internal diameter of the neck of the bottle you propose using, and ask a friend to make it enter the bottle by blowing upon it.
At first sight this seems a very easy task, and your friend at once proceeds to blow strongly upon the cork. This, however, instead of making the cork enter the bottle, causes it to fly out.
Again your friend tries to overcome the troublesome cork, on the next occasion by blowing very gently, but again it flies out ([Fig. 1]).
The explanation of this is as follows:—
In blowing upon the cork, a certain amount of air at the same time enters the bottle, the air in which becomes so compressed that it rapidly ejects the cork. There are, however, three ways in which the refractory cork may be overcome.
Fig. 1.—The refractory cork.
Since you know that by blowing on the cork it is at once ejected, try to achieve success by performing the contrary action—that is, by withdrawing some of the air from the bottle.