Among the many specific concepts the student of physics must learn, perhaps none is so deceptively simple as the frame of reference. On the surface, it seems easy to make observations from a certain point in space and time. Yet, when the implications of this idea are explored, the fuller complexities begin to reveal themselves.

Frame of Reference is one of the basic concepts in Kinematics. Kinematics being based upon frame of reference, provides a great deal about the nature of motion of a body in a given sequence of circumstances. Physics involves the study of our surroundings, a form of analysis where everything is put through a logical reasoning process and often provided a theory for. Motion of object around us like cars, rockets, and plane can be understood through this concept. Relative motion or motion of objects with respect to each other is also described using this concept.

To analyse the motion of a body, first we need to find the location of the body at a certain instant of time. To do this, we have the coordinate system. The system of X, Y and Z axes, which are perpendicular to each other, are used to mark the position of an object in a 3 dimensional space. This frame of 3 axes is the frame of reference, which originates from the interaction of the three axes which is the origin. Now in this 3 dimensional space, we can analyse the position and thus the motion of the object. We can predict its path if it follows a path pattern described periodically.

## What is Frames of Reference in Physics?

Imagine you threw and caught a ball while you were on a train moving at a constant velocity past a station. To you, the ball will simply go vertically up and then down under the influence of gravity. However, if there’s an observer on the station platform, then that person will see the ball travel in a parabola, with a constant horizontal component of velocity equal to the velocity of the train.

So, the different observations occur because the two observers are in different frames of reference. A frame of reference is nothing but a set of coordinates that can be used to determine positions and velocities of objects in that frame; different frames of reference move relative to one another.

Simply put, when you are standing on the ground, that is your frame of reference. Anything that you see, watch, or measure will be compared to the reference point of the ground. If you are standing at the back of a moving truck, the truck is now your frame of reference, and everything will be measured, compared to it.

There are two types of frames of reference:

## Inertial Frame of Reference

A frame of reference that remains at rest or moves with constant velocity with respect to other frames of reference is called Inertial Frame of Reference. An inertial frame of reference has a constant velocity. That is, it is moving at a constant speed in a straight line, or it is standing still. Newton’s laws of motion are valid in all inertial frames of reference. Here, a body does not change due to external forces. All inertial frames of reference are equivalent for the measurement of physical phenomena.

There are several ways to imagine this motion:

• Our earth.
• A space shuttle moving with constant velocity relative to the earth.
• A rocket moving with constant velocity relative to the earth.

## Non-inertial Frame of Reference

A frame of reference is said to be a non-inertial frame of reference when a body, not acted upon by an external force, is accelerated. In a non-inertial frame of reference, Newton’s laws of motion are not valid. It also does not have a constant velocity and is accelerating. There are several ways to imagine this motion:

• The frame could be travelling in a straight line, but be speeding up or slowing down.
• The frame could be travelling along a curved path at a steady speed.
• The frame could be travelling along a curved path and also speeding up or slowing down.

To get a detailed idea about the concepts and solve mind-boggling problems in Kinematics, you can try reading leading author HC Verma’s Concept of Physics in class 11th and 12th. Famous foreign publications in the field of physics include IE Irodov and SS Krotov.

Frame of references is only the beginning to the huge pool of interesting topics such as mechanics, which is extremely important for JEE. Read about how to tackle JEE mechanics here.

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