# Notes and caveats¶

Here are some caveats, quirks, and behaviors to be aware of when working with the physics engine:

1. You can add the same force to an object multiple times with repeated calls to addLinearForce or addAngularForce. The result will be that the total effect will be the effect of the force applied once times the number of times it is applied. Note, however, that to remove the force’s effect on the object, you must call remove*Force the same number of times add*Force was called; each call to remove only removes one instance of the force. Of course, it is more efficient to use a single force with magnitude (n x # of copies) than to use the same force multiple times.

2. If a NodePath that is controlled by an ActorNode also needs collision calculations done upon it, be sure to use the PhysicsCollisionHandler instead of CollisionHandlerPusher. More info can be found in the section on Collision Handlers. If you intend to use a PhysicsCollisionHandler to prevent a model from falling through a floor (for example, if the scene has gravity applied), be sure to look at the friction coefficient options on the PhysicsCollisionHandler.