Consider a watering can hanging from a hook. When displaced from its pivot point, it oscillates similar to a simple pendulum. The watering can is an example of a physical pendulum. It can be modeled as its entire weight acting at its center of mass, which oscillates about the pivot point. Let the distance between the pivot point and the center of mass be L. The oscillation is due to the restoring torque produced by gravity, which can be calculated. If the angle of oscillation is small, the torque is approximated. It can also be written in terms of the pendulum's moment of inertia and angular acceleration. The two expressions give an equation for simple harmonic motion, with the mass replaced by the moment of inertia and the force constant replaced by a product of three terms. So, the angular frequency can be determined, and the time period can be derived. For a simple pendulum, the moment of inertia gives the familiar expression for the time period.