The concepts and theories of modern physics / By J.B. Stallo.

  • John Stallo
Date:
1900
Catalogue details

Licence: In copyright

Credit: The concepts and theories of modern physics / By J.B. Stallo. Source: Wellcome Collection.

    96/376 (page 46)
    the apparent repulsion of the atoms and their reciprocal collisions can he simply referred to an appropriate mo- tion, it being sufficient for this purpose to suppose them to be in rotation. Let us prove this: “ Among the beautiful theorems discovered by Poin- sot respecting the impact of bodies in rotation is found one relating to their reflection from a resisting obstacle. It teaches us that by virtue of its rotation alone a hard and inelastic body can rebound absolutely like a body jierfectly elastic ; more than that: one of these bodies, thrown against a fixed obstacle, is often sent back with a velocity superior to its initial velocity. The profound mathematician shows how this phenomenon, paradoxi- cal as it seems, is due to the transformation of part of its rotatory motion into motion of translation ; whence results an increase of the velocity of the center of grav- ity. According to the ordinary theories of impact, in which no account is taken of the motion of rotation, the preceding proposition is absurd, and nevertheless it is perfectly established. Tims, by the side of cases of ordinary reflection we find the phenomena of progres- nion / we might also, using the expression of Poinsot, call them negative reflections. “ In negative reflection after impact, the center of gravity of the body returns with a velocity superior to that which it had at first. These questions form a wholly now and very interesting branch of mechanics ; they are easily demonstrated by compounding the two movements of rotation and translation, considered with reference to the centers of gravity, of rotation and of ]:)ercussion; and we readily understand that generally it may be said: an impact, whatever it may be, can never simultaneously annihilate in a body the two mo- tions of rotation and of translation; for, when the im-