Unity Game Optimization - Third Edition

Rigidbody active and sleeping states

Every modern physics engine shares a standard optimization technique, where by objects that have come to rest have their internal state changed from an active state to a sleeping state. While Rigidbody is in the sleeping state, little to no processor time will be spent during fixed updates to update the object until an external force or collision event has awoken it.

The value of measurement that is used to determine what at rest means tends to vary among different physics engines; it could be calculated using linear and rotational speed, kinetic energy, momentum, or some other physical properties of Rigidbody. Both of Unity's physics engines work by evaluating the object's mass-normalized kinetic energy, ...