A pendulum in which a particle, attached by a string of constant length to a fixed point, moves in a circular path in a horizontal plane. Suppose that the string has length l and that the string makes a constant angle α‎ with the vertical. The particle moves in a circular path in a horizontal plane a distance d below the fixed point, where d = l cosα‎. The period of the conical pendulum is equal to $2\pi \sqrt{d/g}$.