centrifugal force_.

This force presents its claims to attention in all bodies which revolve
about fixed centers, and sometimes these claims are presented with a
good deal of urgency. At the same time, there is probably no subject,
about which the ideas of men generally are more vague and confused. This
confusion is directly due to the vague manner in which the subject of
centrifugal force is treated, even by our best writers. As would then
naturally be expected, the definitions of it commonly found in our
handbooks are generally indefinite, or misleading, or even absolutely
untrue.

Before we can intelligently consider the principles and methods of
balancing this force, we must get a correct conception of the nature of
the force itself. What, then, is centrifugal force? It is an extremely
simple thing; a very ordinary amount of mechanical intelligence is
sufficient to enable one to form a correct and clear idea of it. This
fact renders it all the more surprising that such inaccurate and
confused language should be employed in its definition. Respecting
writers, also, who use language with precision, and who are profound
masters of this subject, it must be said that, if it had been their
purpose to shroud centrifugal force in mystery, they could hardly have
accomplished this purpose more effectually than they have done, to minds
by whom it was not already well understood.

Let us suppose a body to be moving in a circular path, around a center
to which it is firmly held; and let us, moreover, suppose the impelling
force, by which the body was put in motion, to have ceased; and, also,
that the body encounters no resistance to its motion. It is then, by our
supposition, moving in its circular path with a uniform velocity,
neither accelerated nor retarded. Under these conditions, what is the
force which is being exerted on this body? Clearly, there is only one
such force, and that is, the force which holds it to the center, and
compels it, in its uniform motion, to maintain a fixed distance from
this center. This is what is termed centripetal force. It is obvious,
that the centripetal force, which holds this revolving body _to_ the
center, is the only force which is being exerted upon it.

Where, then, is the centrifugal force? Why, the fact is, there is not
any such thing. In the dynamical sense of the term "force," the sense in
which this term is always understood in ordinary speech, as something
tending to produce mo