Force and weight. Force always pushes toward the beginning of the place where it was born, and weight pushes toward the place of its departure. The places where force is born can be infinite, and the place of weight is one only, that is, the earth.

On the rebound.

m, a b, c d e. As much as a rises after the percussion more than b, so much will b be struck upon the ground farther from c than d was.

a b c d; m n, o p. a-b-c-d are 3 equal spaces in an iron bar. If this iron is bent into a half circle, that third part which lies in the middle of the others becomes as much wider in thickness (o-p) as o-p is made longer than m-n.

On the blow.

a b. Because the time of the blow is indivisible, like the contact that is the cause of that blow, its operation is of such swiftness that the time does not permit that blow to transfer itself into the foundations of the things struck with such speed but that it is already dead in the upper parts. Like the mason who breaks the stone with the hammer in his hand, without violence or harm to that hand. And for this reason the iron a-b, being struck by the blow of the hammer in its upper part a, that part has first obeyed the nature of the blow before [obeying] the nature of transferring it to its base b, whence the extremity widens more than the base; and hence it follows that sculptors do better work in removing [material] from their marbles with the pointed hammer than with the chisel struck by the hammer. Moreover a sharp sword will cut the little loaf in the air.

On the sound made by percussion.

The sound cannot be heard by an ear from so close a proximity that the eye has not first seen the contact of the blow. And the reason is this. If we grant that the time of the blow is indivisible, and that the nature of that blow does not work its dilation in the struck body without time, and that no struck body can resound while the thing that strikes is touching that body, and that the voice does not go from the struck body to the ear without time, you will grant that the striking thing is first separated and divided from the struck thing before that struck thing can take up any resonance in itself; and not taking it up, it cannot give it to the ear.

Proof of the blow, and the difference it has with weight and force.

a c, m n. The blow, because of its very brief, indeed indivisible, life, at once performs in its opposition its great and swift operation, which is finished before it reaches the base of the struck thing; whence for this reason you will find greater widening at the top of the struck thing than at its base. And if you wish to know how much greater is the power of the blow upon the struck thing at its top than at its base, look how much the widening of the base m-n enters into that of the top a-c, and by as much as m-n enters into a-c, by so much will a-c receive in itself greater violence than m-n. And if the said support a-m is pressed by weight or force, m-n will widen as much as a-c, because their powers are slower than that of the blow.