# Galilean Relativity: Can Experiments Tell Motion Relative to Other Frames?

• I
• Alpha1
In summary: In Galilean Relativity, laws of mechanics are invariant across frames. This means that if you had an experiment in one frame and measured the outcome in another frame, the results would be the same. This is called the Principle of Equivalence. This principle is a cornerstone of Galilean Relativity, and it is why you can't use experiments to determine whether you are moving or at rest with respect to another frame.

#### Alpha1

In Galilean Relativity, laws of mechanics are invariant across frames. In all the frames they are the same.

So, in Dynamics and Relativity by W.D.McComb, it is written that this implies you cannot perform any experiment in an inertial frame that can tell whether an inertial frame is moving or at rest with respect to another frame.

My question is suppose laws of Physics are different in different frames, then if we are in a frame, can we perform mechanical experiments to determine its speed with respect to other inertial frames.

If the laws of physics were different between every inertial reference frame depending on speed, there would be measurable consequences.
If some measurable thing did change with your reference frame's speed, then you could tell your speed by measuring that thing.

jfizzix said:
If the laws of physics were different between every inertial reference frame depending on speed, there would be measurable consequences.
If some measurable thing did change with your reference frame's speed, then you could tell your speed by measuring that thing.
Hi , thank you for your response.
The change will happen if the frame of reference in which you, changes its speed. I totally agree we can measure that change.
However, if we are just in our frame, what does it mean to determine the speed of other frame ? We do not even know of their existence
I am not able to understand this.

Imagine that the speed of light varied with direction (i.e. light behaved like a wave in a medium), except in one frame in which it is isotropic. That would hint that there was something special about the frame where the speed is isotropic, and how much the speed varied in your chosen frame would tell you how fast you were going with respect to that special frame.

In our universe, you can't do this (or anything analogous) by any means we are aware of.

## What is Galilean Relativity?

Galilean Relativity is the principle that the laws of physics are the same in all inertial frames of reference. This means that the laws of physics do not depend on the observer's motion or perspective.

## What does "inertial frame of reference" mean?

An inertial frame of reference is a frame of reference that is not accelerating or rotating. In other words, it is a frame of reference in which Newton's First Law of Motion (the law of inertia) holds true.

## What is the difference between Galilean Relativity and Einstein's Theory of General Relativity?

The main difference between Galilean Relativity and Einstein's Theory of General Relativity is that the latter includes the effects of gravity. While Galilean Relativity only applies to inertial frames of reference, Einstein's theory applies to all frames of reference, including non-inertial frames.

## How are experiments used to test the principle of Galilean Relativity?

Experiments can be designed to test the principle of Galilean Relativity by observing the outcomes of physical phenomena in different inertial frames of reference. If the outcomes are consistent, regardless of the frame of reference, then the principle holds true.

## Can experiments determine motion relative to other frames of reference?

No, experiments cannot determine absolute motion or velocity. They can only determine relative motion or velocity between two frames of reference. This is because there is no absolute frame of reference in the universe, according to the principle of Galilean Relativity.