# Reference Frame & Principle of Relativity

In this post, we are going to discuss the reference frame and principle of relativity. The principle of relativity was given by Albert Einstein in 1915.

A reference frame is a space in which we are making observations and measuring physical quantities. There are two types of frames of reference:   the inertial reference frame and the noninertial reference frame.

## Types of Reference Frame

• Inertial Reference Frames are the frame of reference in which Newton’s first law of motion holds i.e. an object at rest and an object in motion remain in motion unless acted by a net force. An inertial reference frame is either at rest or moves with a constant velocity.
• noninertial reference frame is a frame of reference that is accelerating, either in a linear fashion or rotating around some axis.

Examples: Label the different frames of reference:

1. A train moving with constant velocity. (Inertial)
2. A rotating merry-go-round. (Non-Inertial)
3. A turning car with constant speed (Non-Inertial)
4. The rotating Earth (Non-Inertial)

The Principle of Relativity:   The principle of relativity states that the basic laws of physics are the same in all inertial frames of reference. This is as you go from one reference frame to another, things like forces, mass, length, and time do not change.

These quantities are said to be absolute.   Since all the laws of mechanics do not change for the different inertial frames of references, no one inertial reference frame is special in any sense.

Therefore we conclude that:

“All Inertial frames of references are equivalent”.