Frame of reference in physics – Inertial and Non-inertial – eSaral

Class 9-10, JEE & NEET

A non-accelerating frame of reference is called an inertial frame of reference. If you want to learn more about the frame of reference in physics. Then keep reading.

## Inertial and accelerated frames of reference

### (a) Inertial frames of reference:

A non-accelerating frame of reference is called an inertial frame of reference. A frame of reference moving with a constant velocity is an inertial frame of reference.
1. All the fundamental laws of physics have been formulated in respect of the inertial frame of reference.
2. All the fundamental laws of physics can be expressed as having the same mathematical form in all the inertial frames of reference.
3. The mechanical and optical experiments performed in an inertial frame in any direction will always yield the same results. It is called the isotropic property of the inertial frame of reference.

#### Examples of inertial frames of reference:

1. A frame of reference remaining fixed w.r.t. distance stars is an inertial frame of reference.
2. A spaceship moving in outer space without spinning and with its engine cut-off is also an inertial frame of reference.
3. For practical purposes, a frame of reference fixed to the earth can be considered as an inertial frame. Strictly speaking, such a frame of reference is not an inertial frame of reference, because the motion of the earth around the sun is accelerated motion due to its orbital and rotational motion. However, due to negligibly small effects of rotation and orbital motion, the motion of earth may be assumed to be uniform and hence a frame of reference fixed to it may be regarded as an inertial frame of reference.

### (b) Non-inertial frame of reference:

An accelerating frame of reference is called a non-inertial frame of reference.

Newton’s laws of motion are not directly applicable in such frames, before application

Note:

A rotating frame of reference is a non-inertial frame of reference because it is also an accelerating one due to its centripetal acceleration.

## Pseudo force

The force on a body due to the acceleration of non-inertial frame is called fictitious or apparent or pseudo

force and is given by $\overrightarrow{\mathrm{F}}=-\mathrm{m} \overrightarrow{\mathrm{a}_{0}}$, where $\vec{a}_{0}$ is acceleration of non-inertial frame with respect to an inertial frame and m is mass of the particle or body.

The direction of pseudo force must be opposite to the direction of acceleration of the non-inertial frame.

When we draw the free body diagram of a mass, with respect to an inertial frame of reference we apply only the real forces (forces that are actually acting on the mass).

But when the free body diagram is drawn from a non-inertial frame of reference a pseudo force

(in addition to all real forces) has to be applied to make the equation $\overrightarrow{\mathrm{F}}=\mathrm{m} \overrightarrow{\mathrm{a}}$ to be valid in this frame also.

So, that’s all from this article. I hope you get the idea about the frame of reference in physics. If you have any confusion related to this article then feel free to ask in the comments section down below.