Page:The Solar System - Six Lectures - Lowell.djvu/141



sents the body's momentum, and therefore cannot change the area swept out.

When two bodies collide, therefore, they each bring an eternal definite amount of motion to the collision; this amount is unaffected by the shock.

Nor can the mutual attraction of the two bodies themselves alter it; for, since a force is measured by the amount of velocity it can generate in a given time, the velocities generated must be as the opposite masses, and therefore the momentum produced in each be the same.

Let $$ \scriptstyle m$$ and $$\scriptstyle m_1$$ be the masses. Then and and whence or where