# Why observer beside the track is in motion with respect to passenger in a moving train ?

This is what high physics book says:

"For the passenger, the train is stationary and the observer beside the track is in motion."

I don't understand !   If I'm passenger in a moving train, I think observer beside the train track would appear as standing still to me.
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Commented:
The passenger wouldn't appear to be actually moving (as in walking or running) but there position would be changing (i.e. movement). If I am sitting on a chair in the train it is just like sitting on a chair in my house; the chair is not changing position. The train does not appear to be changing position either as it is my environment.

Another way to think of it is sitting still in your house. Your house is moving because of the Earth's rotation but it doesn't feel that way, it feels like you are sitting still in your house.
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Author Commented:
I'm asking about the observe standing beside the train track.  The passenger is in the moving train.

Why observer is moving with respect to passenger ?
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CEOCommented:
Think of it this way...you are on a smooth, smooth running train.  It's so smooth in fact, that you feel no motion at all.  And it's dark (totally dark) inside and out but you do have a window.  Also, you have no idea that you are on a train (scary I know, but trust me on this).  Now someone is outside standing still with a glowing hat on.  They just stand there as you pass.  As you look out the window into the dark (having no idea that you are on a train or even moving) what will that hat look like to you?
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Author Commented:
>>  what will that hat look like to you?
I think when I'm far from the hat, it will look like dim light.  As I get closer to hat, the light will get brighter and brighter.
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CEOCommented:
Yes, it will look like it is moving/flying right past your window (because it is moving based on your position)
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Commented:
The person standing beside the tracks is not motionless.

...I think observer beside the train track would appear as standing still to me.

The observer beside the tracks is in motion at maybe a thousand miles per hour as the Earth rotates. The observer is also in motion at the same speed as the Earth as the Earth revolves around the Sun. The observer is also in motion as the solar system moves around the galaxy. The observer is also in motion as... etc.

A major point to the whole idea is that the way things appear to be in motion or to be "standing still" is nothing but 'appearance'. The way things appear to be is not the same as the way things are.

Imagine yourself to be a couple light years away from the Earth out in open space. There is nothing nearby that you can use to judge whether you are 'moving' or not. You don't feel like you're moving. If you measure light from a nearby star and determine that the light is red-shifted, how do you decide if the star is moving away from you or if the star is 'standing still' and you are moving away from the star?

The point is that the math of physics works to give the same results no matter which way you decide.

Tom
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CEOCommented:
Thanks for the points!

One last thing...just to make the distinction here:  we are talking about relative motion, right?  Well, relative motion still comes into play even when two objects see no movement between themselves.  For example, two fighter jets flying in perfect formation with one another appear not to be moving at all (relative to each other, ie. 0 mph)...even though they may be flying 500 mph with respect to the ground and 1,000 mph with respect to another jet going 500 mph strait at them head-on.
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Commented:
Another perspective.....

Imagine that there are three people: you (sitting in the train), another passenger standing in front of you, and an observer standing on the ground outside the train.

When the train is traveling along the tracks, which of the other two individuals do you see as standing still?  The position of the individual in the train stays the same (from your point of view) as time passes, but the one outside keeps changing.
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