rigid_body_sleeping

When a dynamic rigid-body doesn't move (or moves very slowly) during a few seconds, it will be marked as sleeping by the physics pipeline. Rigid-bodies marked as sleeping are no longer simulated by the physics engine until they are woken up. That way the physics engine doesn't waste any computational resources simulating objects that don't actually move. They are woken up automatically whenever another non-sleeping rigid-body starts interacting with them (either with a joint, or with one of its attached colliders generating contacts).

However, a sleeping rigid-body won't respond to any user action. This is why it is possible to wake-up the rigid-body manually with RigidBody.wakeUp(). Some rigid-body methods take an additional wakeUp boolean argument that, if true, ensures that the rigid-body wakes up before the action takes place. For example:

• RigidBody.addForce(force, true) will wake-up the rigid-body before adding the force.
• World.removeJoint(joint, true) will wake-up the two rigid-bodies attached by the removed joints.
• World.removeCollider(collider, true) will wake-up the rigid-body the removed collider is attached to.

Unless you want to achieve special effects, it is recommended to always set the wakeUp argument to true. One example of case where setting the argument of wakeUp to false makes sense is to simulate a custom constant gravity with RigidBody.addForce(force, false). This will result in the force being applied to the rigid-body, but will allow the rigid-body to fall asleep if it reaches a dynamic equilibrium.