To Cut a String With Your Hands.
With a little practice, and some briskness of movement, you may be able to break a string of considerable thickness by proceeding as follows:
Wind the string round your left hand, so as to make a loop, as shown in the figure. Pass it three or four times round the fingers to insure the solidity of the loop. Seize firmly the other end of the string with your right hand, around which you wind it three or four times, then give a brisk pull. The string will be clean cut at the junction of the loop in the left hand.
When the knack is well acquired, one may break the string on two fingers only, by following always the same theory as above.
The Rebound.
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.