If you have objects that use Unity’s physics system, via a rigidbody component, you can add forces to them to get them to move. Forces can be added using one of four different ‘modes’. The names of these modes aren’t very enlightening and I don’t think the Unity3D documentation is very clear about their differences. For my own reference, and in case it helps others, this is what I’ve figured out.
- ForceMode.Force. If the AddForce call occurs in a FixedUpdate loop, the full force supplied to the AddForce call will only have been exerted on the rigidbody after one second. Think of it as ‘Force exerted per second’
- ForceMode.Acceleration. Like ForceMode.Force, except the object’s mass is ignored. The resulting movement will be as though the object has a mass of 1. The following lines will give the same result
rigidbody.AddForce((Vector3.forward * 10),ForceMode.Force); rigidbody.AddForce((Vector3.forward * 10)/rigidbody.mass,ForceMode.Acceleration);
- ForceMode.Impulse. The entirety of the force vector supplied to the AddForce call will be applied all at once, immediately.
- ForceMode.VelocityChange. Like ForceMode.Impulse except the object’s mass is ignored. So the following lines give the same result:
rigidbody.AddForce((Vector3.forward * 10),ForceMode.Impulse); rigidbody.AddForce((Vector3.forward * 10)/rigidbody.mass,ForceMode.VelocityChange);
I made a little test to verify this. The script demonstrates how the ForceModes work by canceling out their differences through modifying the values passed to the AddForce call.