# Inertial vs non inertial frames

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• rudransh verma
In summary, the frame with respect to which we decide whether a frame is inertial or not is the particle, not the frame with respect to which we observe the motion.
rudransh verma
Gold Member

I previously thought Earth is inertial frame and relative to Earth non accelerating frames are inertial too. But after watching this video, I came to know that it’s not the frame with respect to which we decide whether a frame is inertial or not. It’s the particle.
When a particle is not accelerating the frame is inertial. When it’s accelerating frame is non inertial.
But how the author is saying there is acceleration even when the net force is zero? I don’t get that part.
Also for example we take Earth and lift example. If our lift is accelerating then what does that make the earth, a non inertial frame or inertial ?

vcsharp2003
rudransh verma said:
I previously thought Earth is inertial frame

It can't be since it is rotating. Rotating reference frames are not inertial. But sometimes we can neglect those effect, and treat frame connected with Earth as inertial, but that is an approximation.

vcsharp2003 and vanhees71
Another very illuminating movie, one of my favorites, is

rudransh verma and Steve4Physics
rudransh verma said:
Also for example we take Earth and lift example. If our lift is accelerating then what does that make the earth, a non inertial frame or inertial ?
Part of the skill of physics/engineering is to know how to think about a problem.

Suppose you are doing experiments in a lab’ with colliding objects on an air-track. The fact that the Earth is rotating (so is non-inertial) is irrelevant – the effects on the experimental results are too small to have any detectable effects. You are therefore justified in treating the Earth as an inertial frame.

But if you are a meteorologist analysing large-scale patterns of air flow in the atmosphere., you cannot ignore the earth’s rotation. You must treat the Earth as a non-inertial frame. (Read about Coriolis force if you are not already familiar with it.)

rudransh verma and vanhees71

## What is the difference between inertial and non-inertial frames?

Inertial frames are reference frames in which Newton's laws of motion hold true, and objects move at a constant velocity or remain at rest unless acted upon by an external force. Non-inertial frames are reference frames that are accelerating or rotating, and therefore, Newton's laws do not hold true.

## What is an example of an inertial frame?

An example of an inertial frame is a train moving at a constant velocity on a straight track. As long as there are no external forces acting on the train, objects inside the train will also move at a constant velocity or remain at rest.

## What is an example of a non-inertial frame?

An example of a non-inertial frame is a car making a sharp turn. The car is accelerating and therefore, objects inside the car will appear to experience a force in the direction opposite to the turn.

## Can an object be in both an inertial and non-inertial frame at the same time?

No, an object can only be in one frame at a time. However, an observer in an inertial frame can see an object in a non-inertial frame and vice versa.

## Why is it important to distinguish between inertial and non-inertial frames?

It is important to distinguish between these frames because the laws of physics behave differently in each frame. In inertial frames, Newton's laws hold true and are used to analyze motion, while in non-inertial frames, additional forces must be taken into account. This is crucial in fields such as mechanics and astrophysics where precise calculations are necessary.

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