and I shall not further refer to them.

Two very different forces, or manifestations of force, are developed by
the motion of bodies. These are


MOMENTUM AND CENTRIFUGAL FORCE.

The first of these forces is exerted by every moving body, whatever the
nature of the path in which it is moving, and always in the direction of
its motion. The latter force is exerted only by bodies whose path is a
circle, or a curve of some form, about a central body or point, to which
it is held, and this force is always at right angles with the direction
of motion of the body.

Respecting momentum, I wish only to call your attention to a single
fact, which will become of importance in the course of our discussion.
Experiments on falling bodies, as well as all experience, show that the
velocity of every moving body is the product of two factors, which must
combine to produce it. Those factors are force and distance. In order to
impart motion to the body, force must act through distance. These two
factors may be combined in any proportions whatever. The velocity
imparted to the body will vary as the square root of their product.
Thus, in the case of any given body,

Let force 1, acting through distance 1, impart velocity 1.
Then " 1, " " " 4, will " " 2, or
" 2, " " " 2, " " " 2, or
" 4, " " " 1, " " " 2;
And " 1, " " " 9, " " " 3, or