# Frame of reference

In physics, a frame of reference is the point from which an observer views a system. There are two types of reference frames, inertial frames and non-inertial frames.

Inertial frames are frames that have linear and angular acceleration equal to zero. Newton's laws of motion only apply in inertial frames, although in many cases they are a close enough approximation in a non-inertial reference frame (for example, the earth is not an inertial reference frame as it is both rotating about its own axis and orbiting the sun and therefore accelerating).

Non inertial frames are frames that have either angular or linear (or both) accelerations that are not equal to zero. Newton's laws of motion do not apply in these frames. Objects observed from within appear to violate Newton's laws of motion. Fictitious forces such as the Coriolis effect and centripetal acceleration can be explained through the use of non inertial reference frames. Both are caused by the acceleration of the reference frame itself.