# Inertial and non inertial frame of reference

• officialmanojsh
In summary, inertial and non-inertial frame of references are two concepts that determine whether the law of inertia is valid or not within a coordinate system. An inertial frame of reference is one where the law of inertia holds true, while a non-inertial frame of reference is one where the law of inertia is not valid due to acceleration. This can be observed through the movement of objects, such as a helium balloon on a string, within these frames of reference. The law of inertia states that a body will continue to move in a straight line at a constant speed unless acted upon by an external force.
officialmanojsh
When I was surfing on a group in Facebook, I found two concepts very difficult to understand by reading the discussions in comments. Those concepts are inertial and non inertial frame of reference. Please make me understand these two concepts in simple words. Please don't suggest links as I can't understand complex and new English words in a sentence. So please help me understand. :)

An inertial frame of reference is a coordinate system in which the law of inertia is valid. If a coordinate system is accelerating then the law of inertia is not valid within the system and is therefore a non-inertial frame.

officialmanojsh said:
When I was surfing on a group in Facebook, I found two concepts very difficult to understand by reading the discussions in comments. Those concepts are inertial and non inertial frame of reference. Please make me understand these two concepts in simple words. Please don't suggest links as I can't understand complex and new English words in a sentence. So please help me understand. :)
If you are in a car and the car is traveling straight ahead at a constant speed, then you are in an inertial frame of reference. If you are holding the string from a helium balloon in your hand, the string will be vertical, and the balloon will stay where it is.

If you are in a car, and the car is accelerating forward or traveling around a curve, then you are in an accelerating, non-inertial frame of reference. During the time that either of these accelerations is occurring, the string on the balloon will not be vertical. In the case where you are accelerating forward, the balloon will move toward the back, and in the case where you are going around a right turn, the balloon will move toward the left.

Chet

Vishwaas
brainpushups said:
An inertial frame of reference is a coordinate system in which the law of inertia is valid. If a coordinate system is accelerating then the law of inertia is not valid within the system and is therefore a non-inertial frame.
Chestermiller said:
If you are in a car and the car is traveling straight ahead at a constant speed, then you are in an inertial frame of reference. If you are holding the string from a helium balloon in your hand, the string will be vertical, and the balloon will stay where it is.

If you are in a car, and the car is accelerating forward or traveling around a curve, then you are in an accelerating, non-inertial frame of reference. During the time that either of these accelerations is occurring, the string on the balloon will not be vertical. In the case where you are accelerating forward, the balloon will move toward the back, and in the case where you are going around a right turn, the balloon will move toward the left.

Chet
What does law of inertia say ?

officialmanojsh said:
What does law of inertia say ?
If a body is traveling in a straight line at constant speed, it is experiencing no net external force. But why do I have to tell you this? Why can't you just Google "law of inertia" and find out for yourself? Or look in you textbook?

Chet

## 1. What is an inertial frame of reference?

An inertial frame of reference is a frame of reference in which Newton's first law of motion holds true. This means that an object at rest will remain at rest, and an object in motion will continue to move at a constant velocity, unless acted upon by an external force. In other words, there is no acceleration in an inertial frame of reference unless there is an external force acting on the object.

## 2. How is a non-inertial frame of reference different from an inertial frame?

A non-inertial frame of reference is a frame of reference in which Newton's first law of motion does not hold true. This means that an object at rest may not remain at rest, and an object in motion may not continue to move at a constant velocity, even if no external forces are acting on it. Examples of non-inertial frames of reference include a rotating frame or an accelerating frame.

## 3. Why are inertial frames of reference important in physics?

Inertial frames of reference are important in physics because they provide a framework for understanding and analyzing motion. By using an inertial frame of reference, we can accurately measure and predict the motion of objects without the influence of external forces. This allows us to study and understand the fundamental laws of motion, such as Newton's laws.

## 4. How do you determine if a frame of reference is inertial or non-inertial?

To determine if a frame of reference is inertial or non-inertial, you can perform a thought experiment. If an object appears to be accelerating or moving in a curved path in the frame of reference, then it is a non-inertial frame. If the object appears to be moving with a constant velocity, then it is an inertial frame of reference. Another way to determine this is by analyzing the forces acting on the object in the frame of reference. If there are no external forces, then it is an inertial frame.

## 5. How does the concept of inertial frames of reference relate to Einstein's theory of relativity?

In Einstein's theory of relativity, the concept of inertial frames of reference is expanded upon. It is now understood that there is no absolute frame of reference, and all frames of reference are equally valid. This means that the laws of physics, including Newton's laws of motion, are the same in all inertial frames of reference. Additionally, the theory of relativity introduces the concept of non-inertial frames of reference that are affected by gravity, known as accelerated frames, which must be taken into account when studying motion and forces in the universe.

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