Inertial and Non-Inertial Frame of Reference

Inertial and Non-Inertial Frame of Reference are two frames of reference based on the validity of Newton’s Laws of motion on them. Frames of reference play a fundamental role in physics, to the analyze object motion, investigation of forces and interactions, and understanding of relativity principles. They establish a standardized framework for describing physical phenomena and predicting the behavior of systems.

In this article, we will learn in detail about inertial and non-inertial frame of reference with a brief introduction of frame of reference.

What is a Frame of Reference?

A frame of reference is a coordinate system or set of axes used to define the position, orientation, and motion of objects in space and time. It serves as a reference point from which measurements and observations are made.

A frame of reference is required to measure various quantities, such as displacement, velocity, and acceleration. Physical reference points in the frame of reference act as a unique means of fixing the coordinate system and standardizing measurements.

Consider an example where two one persons are there. One is present in a moving car and other is observing him. The person inside the car is at rest, but its’s moving for the person outside the car because the car is moving so he will say that he is moving with some velocity in some direction. So, if we want to calculate it’s velocity or its’s direction, we need to define some frame of reference that in reference to this frame this person is moving. And if take the reference to the car, only car is moving and the person inside the cart is still.

Types of Frame of Reference

There are two types of Frame of Reference:

• Inertial Frame of Reference
• Non-Inertial Frame of Reference

What is Inertial Frame of Reference?

Inertial frames of reference are those in which Newton’s first law is valid. This implies that a body will remain at rest or in uniform motion in the absence of any external forces acting on it.

An inertial frame of reference is the type of frame where Newton’s laws are true. This implies that if no external force is applied on an object, it will continue to stay in uniform motion or state of rest.

Since we first take a reference frame to be the inertial frame of reference, the term “inertial frame” is actually relative. Accordingly, a detailed meaning of an inertial frame would be: An inertial frame is one that is either stationary or travels at a constant speed in relation to an assumed inertial reference frame. It means that the net force acting on the body is zero and the body is not accelerating.

Inertia

Inertia is a property of matter in which an object that is at rest remain at rest and an object in motion, remains in motion until and unless any external force acts upon it.

Example of Inertial Frame of Reference

• A platform at a railway station is an example of an inertial reference system. The platform satisfies the requirement of not speeding since it remains stationary. The law of inertia governs how things move on the platform.
• Rolling Ball: Until an outside force is provided, a ball rolling across the platform will keep rolling at the same speed. Without an outside force, the bench on the platform will not move. This holds true for the whole platform.
• Inertia is also applied by trains approaching the platform. It only slows down when the braking power is applied. It will move through the platform at a steady speed in the absence of this force.

What is Non-Inertial Frame of Reference

A frame that is accelerated relative to the assumed inertial frame of reference is called a non-inertial frame. In non-inertial frame, Newton’s laws of motion are not followed. The non-inertial frame of reference moves faster than the expected inertial frame of reference. Either you can accelerate while maintaining a constant speed in a non-inertial coordinate system, or you can follow a circular route while maintaining a constant speed.

A non-inertial frame of reference is one that exhibit acceleration because of any change in speed or direction.

When compared to the usual inertial coordinate system, the non-inertial coordinate system is an accelerated coordinate system. Accelerometers in these kinds of frames typically detect non-zero accelerometers when the frame is unbalanced.

Example of Non-Inertial Frame of Reference

• For an instance, when you’re stopped at a traffic signal in your car. The vehicle is not moving. The automobile accelerates as the traffic light turns green. The vehicle is in a non-inertial frame of reference during this acceleration.
• Lift moving up and down

Note: Earth is not an example of inertial frame of reference but rather it is an inertial frame of reference. This is because earth rotates on its axis around the sun. However, when motion such as walking etc,. is considered then earth can be considered as an inertial frame of reference.

Difference Between Inertial and Non-Inertial Frame of Reference

The difference between Inertial and non-inertial frame of reference is tabulated below:

Inertial Frame of Reference	Non-Inertial Frame of Reference
Frame of reference either at rest or moving with constant speed.	Frame of reference having uniform linear acceleration or rotating at uniform speed.
Acceleration in this frame of reference is always zero.	Some acceleration is there in this frame of reference .
It obeys Newton’s law.	It does not obeys Newton’s law.
Example: Train moving with constant velocity is inertial frame of reference.	Example: A freely falling elevator is considered as non-intertial frame of reference.

FAQs on Inertial and Non-Inertial Frame of Reference

What is meant by a frame of reference?

A frame of reference is a coordinate system or set of axes used to define the position, orientation, and motion of objects in space and time.

What are the two types of frames of reference?

The frame of reference is of two types:

• inertial frame of reference
• non-inertial frame of reference.

What is meant by an inertial frame of reference?

An inertial frame of reference is the type of frame where Newtonian laws are true. This implies that if no outside force is exerted on an object, it will continue to stay in uniform motion or state of rest.

What is meant by an non-inertial frame of reference?

A non-inertial frame of reference can be defined as a frame that is in the state of acceleration relative to the considered inertial reference frame. Newtonian laws are not followed in these reference frames.

Is Sun an inertial frame of reference?

The sun is an inertial frame of reference for the earth as with respect to the earth; the sun is not accelerating.

Is free fall an inertial frame?

Yes, free fall can be considered an inertial frame. In free fall, an object is falling under the influence of gravity alone, and in the absence of other forces (such as air resistance), it experiences uniform acceleration due to gravity.

Is non-inertial frame accelerated?

Yes, a non-inertial frame is accelerated.