# What is frame of reference in physics class 11

Physics is the study of the natural phenomena that occur in the universe. To understand and explain these phenomena, we need to use some concepts and tools that help us describe the physical reality. One of these tools is the **frame of reference**.

## What is a Frame of Reference?

A frame of reference in physics is a system of coordinates or axes that can be used to describe the position, orientation, motion, and other properties of objects relative to an observer or a measurement apparatus. There are different types of frames of reference, such as observational, measurement, or inertial, that may depend on the state of motion of the observer or the object.

For example, suppose you are standing on a train platform and you see a train moving with a constant speed. You can use the platform as your frame of reference and say that the train has a certain velocity relative to you. But if you are inside the train, you can use the train as your frame of reference and say that the platform has a certain velocity relative to you. Both frames of reference are valid, but they give different descriptions of the same situation.

## Types of Frame of Reference

Once we have chosen our reference points and coordinate system, we can classify the frames of reference into two main types: **inertial** and **non-inertial**.

### Inertial Frame of Reference

An inertial frame of reference is a frame where Newton’s laws of motion hold true. That means if no external force is acting on a body, it will stay at rest or remain in uniform motion. An inertial frame of reference is also called a **Galilean** or **Newtonian** frame.

For example, if you are in a car that is moving with a constant speed on a straight road, you can use the car as an inertial frame of reference. In this frame, any object inside the car that is not attached to it will remain at rest or move with a constant velocity unless acted upon by an external force.

### Non-inertial Frame of Reference

A non-inertial frame of reference is a frame that is accelerated with respect to an inertial frame of reference. Newton’s laws of motion do not hold true in these frames. To make them hold true, we need to introduce some fictitious forces or pseudo forces that account for the acceleration of the frame. A non-inertial frame of reference is also called an **accelerated** or **rotating** frame.

For example, if you are in a car that is speeding up or slowing down on a curved road, you cannot use the car as an inertial frame of reference. In this frame, any object inside the car that is not attached to it will appear to be acted upon by some mysterious forces that are not due to any real interaction. These forces are called **centrifugal**, **Coriolis**, or **Euler** forces depending on the type and direction of acceleration.

## Why is Frame of Reference Important?

The concept of frame of reference is important because it helps us to understand and compare the relative motion of objects in different situations. It also helps us to apply the laws and principles of physics consistently and correctly in different contexts.

For example, if you want to calculate the kinetic energy or momentum of an object, you need to know its velocity relative to a certain frame of reference. If you change the frame of reference, the velocity will change and so will the kinetic energy or momentum. Similarly, if you want to analyze the forces acting on an object, you need to choose an appropriate frame of reference that simplifies your calculations and avoids unnecessary complications.

## How to Choose a Frame of Reference?

There is no absolute or universal frame of reference that applies to all situations. The choice of frame of reference depends on your purpose and convenience. However, there are some general guidelines that can help you choose a suitable frame of reference for your problem:

Choose an inertial frame of reference whenever possible, as it makes your calculations easier and avoids pseudo forces.

Choose a frame of reference that is fixed or moving with constant velocity with respect to your assumed inertial frame.

Choose a frame of reference that includes all the relevant objects and interactions in your problem.

Choose a frame of reference that has simple and symmetrical coordinate axes that align with the direction or plane of motion.

Choose a frame of reference that minimizes the number and magnitude of variables and constants in your equations.

## Example: Frame of Reference for Projectile Motion

Let us consider an example where we need to choose a suitable frame of reference for analyzing projectile motion. Projectile motion is the motion of an object thrown into the air with some initial velocity at some angle from the horizontal.

To study projectile motion, we can choose the following frame of reference:

The origin of the frame is at the point where the object is thrown.

The x-axis is horizontal and points in the direction of the initial velocity.

The y-axis is vertical and points upwards.

The z-axis is perpendicular to the x-y plane and points out of the page.

This frame of reference is an inertial frame, as it is fixed with respect to the earth (assuming the earth is an inertial frame). It also includes all the relevant objects and interactions, such as the object, the initial velocity, the angle, the gravity, and the air resistance. It also has simple and symmetrical coordinate axes that align with the direction or plane of motion. It also minimizes the number and magnitude of variables and constants in our equations.

Using this frame of reference, we can write the equations of motion for projectile motion as follows:

## Conclusion

In this blog post, we have learned about the concept of frame of reference in physics. We have seen what a frame of reference is, what are its types, why it is important, and how to choose it. We have also seen an example of choosing a frame of reference for projectile motion. We hope this post has helped you to understand and appreciate this fundamental tool of physics.