# Just fun thought on Galilean relativity

1. Dec 23, 2015

### Alpharup

I thought of explaining galilean relativity to a layman like this:

"A person is heavily drunk and he revolves, revolves and revolves. He shouts," The world is revolving around me". You are bystander and u say," you drankard, the world is not revolving, but you are the one who is going in rounds and rounds". Who is correct? You or the drunkard:D;).....Well, galilean relativity says both are right. For him, he is at rest and all the objects are revolving. For you, you are at rest and see him revolving "

My idea is to present him that different frames yield different results( one is drunkard's frame and another is layman's frame)

Is this example right?

2. Dec 23, 2015

### phinds

Sure, it's right but it seems to me that a more straightforward and common explanation is your being on a train in a station and the train next to you starts to move. But who REALLY started to move, you or them?

3. Dec 23, 2015

### Alpharup

Another one....you are doing pushups. ...either you are doing pushups or the earth is moving towards and away from you.

4. Dec 23, 2015

### Buzz Bloom

Hi Alpharup:

I think Galilean relativity applies only to linear motion, and not rotational motion. Perhaps if I am wrong about this, someone will correct my error.

See http://physics.ucr.edu/~wudka/Physics7/Notes_www/node47.html . Here is a quote:
Generalizing these observations Galileo postulated his relativity hypothesis:
any two observers moving at constant speed and direction with respect to one another will obtain the same results for all mechanical experiments

Regards,
Buzz

5. Dec 23, 2015

### Alpharup

No I am not talking about results in different frames. What I am talking about is intuition behind relativity. People have a preconceived notion of right observation and wrong observation. Just to explain them, I asked this. Also, relativity apples to rotational motion as well

6. Dec 23, 2015

### phinds

Nah, NOBODY is going to believe that one; everybody's muscles tell them THEY are moving

7. Dec 23, 2015

### Alpharup

Haha....

8. Dec 23, 2015

### Buzz Bloom

Hi Alpharup:

I apologize for misunderstanding you. Since the title of the thread said "Galilean", I thought your intention was to provide examples to explain Galileo's concept.

Regards,
Buzz

9. Dec 23, 2015

### Helios

There's something like this about a man, a tree, and a squirrel. A man walks once around a tree and the squirrel scurries to keep the tree in between him and the man. Has the man walked around the squirrel?

10. Dec 23, 2015

### phinds

If you think about it at all, it is clear that no he has not. The man ALWAYS sees the squirrel 90 degrees off of one shoulder (which one depends on which way they are circling) so this is not at all a good example of the relativity of movement.

11. Dec 23, 2015

### Helios

It's a wondrous example of the relativity of movement ( if you think about it at all ). Others would say the man has covered north, west, south, and east making one once-around. It is the choice of axis of rotation that distinguishes the different meanings of ‘going around.’ It is a choice between two reference frames.

12. Jan 3, 2016

### collinsmark

If I may make a recommendation, I'd avoid using rotating reference frames when explaining Galilean relativity. At least avoid it at the beginning of the explanation. You can always bring it up later after the basics are firmly established.

Even in Galilean relativity, there exists concepts such as "inertial frames," frames that might have differing relative velocities but are not rotating or accelerating. I'd start with those.

I say that because a person can tell if he or she is rotating. For example, if a person is rotating around their center, they would feel a centrifugal force that might cause their arms to extend outwards. The characteristics of this force are quantifiable and predictable. And the person would not feel this force if not rotating, but rather that other people/things were revolving around him or her.

There's some very colorful history behind this, most notably from Newton's bucket argument. Even today, with general relativity and modern physics, the solution to the argument is not wholly clear [when applied to all the matter in the universe] (although most physicists today would probably side on rotational motion not being relative, but rather absolute).

I'm not saying one shouldn't discuss the relative aspects of rotational motion; it is a fascinating topic -- certainly worthy of discussion. Just realize that if you bring up rotational motion being relative, you're opening up a whole can of worms.

Last edited: Jan 3, 2016