Drawing of an apparatus for demonstrating the physics of the equatorial bulge of a rotating planet. The oval is a spring-metal band. The elasticity of the spring-metal tends to pull the band towards a circular shape. When the device is spun up, the torque increases the energy. Half the energy goes into increasing the rotational energy of the spring-metal band, the other half goes into potential energy of the elastic deformation of the band.

When the device is no longer driven, and energy is dissipating due to friction, the spring metal band models the equilibrium that determines the shape of the Earth. Friction dissipates kinetic energy. At the same time the kinetic energy is to some extent replenished by the contraction of the spring-metal band. Due to the contraction, the angular velocity decreases less than would be the case with a solid object that is losing energy through friction.