Changes the strength of the global force. For forces that fade this will be the strength at 1 unit from the force position.
The force is in Newtons, and is similar in size to gravity except that it is affected by the mass of the object. For example, for an object of mass of 1 kg and a force of 10 newtons will affect the object in the same way as gravity set at 10 m/s^2. For a mass of 2 kg it is harder to move, so a force of 10 Newtons would be half as effective at moving the object as gravity at 10m/s^2.
SetPhysicsForcePower( iForceIndex, power )