To the extremity of a string about 18 in. in length attach a chain about 15 in. in length, the extremities of which are united. Holding the string vertically between the fingers, give it a rapid rotary motion. The chain will first open out as seen at A of the figure. Upon increasing the velocity of rotation, it will be thrown out farther and farther until it finally forms a circle in a horizontal plane. In this motion, the string forms a sort of conoidal surface, distended by centrifugal force.

B of the figure gives the exact aspect that the arrangement offers to the eye during the revolution. In the same way, a penholder attached by one of its extremities to a string assumes an almost horizontal position.

This experiment illustrates the principle of centrifugal force.