We have been supposing a body to be firmly held to the center, so as to be compelled to revolve about it in a fixed path.  But the bond which holds it to the center may be elastic, and in that case, if the centrifugal force is sufficient, the body will be drawn from the center, stretching the elastic bond.  It may be asked if this does not show centrifugal force to be a force tending to produce motion from the center.  This question is answered by describing the action which really takes place.  The revolving body is now imperfectly deflected.  The bond is not strong enough to compel it to leave its direct line of motion, and so it advances a certain distance along this tangential line.  This advance brings the body into a larger circle, and by this enlargement of the circle, assuming the rate of revolution to be maintained, its centrifugal force is proportionately increased.  The deflecting power exerted by the elastic bond is also increased by its elongation.  If this increase of deflecting force is no greater than the increase of centrifugal force, then the body will continue on in its direct path; and when the limit of its elasticity is reached, the deflecting bond will be broken.  If, however, the strength of the deflecting bond is increased by its elongation in a more rapid ratio than the centrifugal force is increased by the enlargement of the circle, then a point will be reached in which the centripetal force will be sufficient to compel the body to move again in the circular path.

Sometimes the centripetal force is weak, and opportunity is afforded to observe this action, and see its character exhibited.  A common example of weak centripetal force is the adhesion of water to the face of a revolving grindstone.  Here we see the deflecting force to become insufficient to compel the drops of water longer to leave their direct paths, and so these do not longer leave their direct paths, but move on in those paths, with the velocity they have at the instant of leaving the stone, flying off on tangential lines.

If, however, a fluid be poured on the side of the revolving wheel near the axis, it will move out to the rim on radial lines, as may be observed on car wheels universally.  The radial lines of black oil on these wheels look very much as if centrifugal force actually did produce motion, or had at least a very decided tendency to produce motion, in the radial direction.  This interesting action calls for explanation.  In this action the oil moves outward gradually, or by inconceivably minute steps.  Its adhesion being overcome in the least possible degree, it moves in the same degree tangentially.  In so doing it comes in contact with a point of the surface which has a motion more rapid than its own.  Its inertia has now to be overcome, in the same degree in which it had overcome the adhesion.  Motion in the radial direction is the result of these two actions, namely, leaving the first point of contact tangentially and receiving an acceleration of its motion,