# Explain the concept of non accelerated frames.

## Question:

Explain the concept of non accelerated frames.

## Inertial and Non-inertial Frames

A frame of reference moving with a constant velocity is called an inertial frame. When motion is analyzed in an inertial frame, Newton's laws may be directly applied. By identifying the contact forces and long-range forces the acceleration may be determined and then the kinematical relations may be used.

In an accelerated frame of reference or a non-inertial frame, Newton's laws are not directly applicable. An object of mass M will experience a fictitious or pseudo force {eq}\displaystyle {- Ma} {/eq} if the acceleration of the frame is {eq}\displaystyle {a} {/eq}. This is what happens when you are inside a bus which suddenly accelerates forward. You are thrown backward even though there is no visible agency pushing you backward. Once the fictitious forces are taken into consideration over and above the contact and long-range forces then Newton's laws will work fine. Now acceleration can arise either by the change in the magnitude of the velocity or by the change in direction. In a uniformly rotating frame of reference, acceleration arises on account of the change in direction. Now two fictitious forces arise. They are the centrifugal force and the Coriolis force. Since the earth is rotating about its own axis once in 24 hours the earth frame of reference is a rotating frame. Therefore we experience both the centrifugal force and the Coriolis force. But these pale in comparison to the gravity of the earth.

Thus in a non-accelerated or inertial frame mechanics is relatively simple and falls entirely within the ambit of Newton's laws. There are no mysterious pseudo forces. The frame of reference provided by a distant star is for all practical purposes, a non-accelerated or inertial frame. This is because the star is so far away that it doesn't interact with anything and therefore the star has no acceleration. Of course, this is an idealization. As a matter of fact, the perfectly inertial frame is well nigh impossible since the entire stuff of the universe is in mutual interaction with each other. But it is a very good approximation.