# Non-inertial reference frame

1. Nov 20, 2006

### ergonomics

dealing with non-inertial rotating reference frames, real forces such as the centripetal force need to be taken into account,or only the forces that can be really observed within the frame?

because from the perspective of the rotating frame, objects should be at rest. it only appears logical to replace the centripetal force with the centrifugal force when dealing in rotating frames.

2. Nov 20, 2006

### Staff: Mentor

Real forces always count. "Real" forces have agents as opposed to "fictitious" inertial forces that are artifacts of using a noninertial frame of reference.

Note: "centripetal" force just means a force that acts toward the center (or the net force acting toward the center)--it's not a separate kind of force.

Example: Imagine a spinning turntable on which a small block sits. The block spins along with the turntable. From an inertial frame, the block is centripetally accelerated; the centripetal force is the friction between turntable and block.

From the rotating frame that very real friction force still acts, but now the acceleration is zero: In addition to the real friction force, one needs to add the "fictitious" centrifugal force in order to use Newton's laws.