What Determines the Speed of a Spacecraft in Special Relativity?

[Delzac]

Homework Statement

Usually in physics problem on special relativity, the state that this particular spaceship is traveling at, say, 0.6c.

Question is, where does this 0.6c come from? If the speedometer in the cockpit reads 0.6c, does it mean that the observer will look and think that it is traveling at 0.6 c?

I suppose spacecraft determines its speed with reference to its surrounding, that's how we all determine your own speed isn't it? From a 1meter mark to another, how long did it take. Craft determines its speed via this method, the environment outside would length contract wouldn't it? So is the velocity from the 2 different frame the same?

Lorentz Velocity Transform tells me that it would, cause,

$$u'_x = 0$$

Any ideas? Any help will be appreciated.

 

[DaveC426913]

If we say a craft is moving at .6c, that will be relative to the observer.
If the occupant wished to know what his speed was relative to his surroundings, he would have to take into account that his surroundings will be compressed in the direction of his travel. He's also have to take into account time dilation.

 

[Delzac]

Okay thanks, got it.

 

[DaveC426913]

Okay thanks, got it.

Really? No argument?

I think PF is going to explode.

 

[Delzac]

Anomalies sometimes do surface.

Or why not take it that you have done a wonderful work explaining the concept to me.^^