
#1
Feb1413, 12:29 PM

P: 6

Is this statement true? The speed of light (about 300,000,000 meters per second) is the same for all observers, whether or not they're moving.
If so could someone please explain it to me, because it was my understanding that if an object was moving at a constant velocity it would appear to be travelling slower to an observer which is stationary than an observer travelling at any constant velocity. Found on http://science.howstuffworks.com/warpspeed2.htm Thanks 



#2
Feb1413, 12:44 PM

PF Gold
P: 4,522





#3
Feb1413, 01:00 PM

P: 1

The statement is false. The speed of light is constant (299,792,458 m/s) regardless of reference frame and velocity of an observer.




#4
Feb1413, 01:14 PM

P: 6

Eisteins theory of relativityread the question more thoroughly please. 



#5
Feb1413, 01:21 PM

Mentor
P: 28,795

So you need to thoroughly read your post and make sure you convey your message clearly. IF that link wasn't your reference, what is the purpose for it being presented there? Zz. 



#6
Feb1413, 01:21 PM

P: 6





#7
Feb1413, 01:23 PM

Sci Advisor
Thanks
P: 2,951

Two interesting things about this formula: 1) For speeds that are small compared with the speed of light, it comes out REALLY close to the vu that you expected; that's why you've never noticed. 2) If v=c (that is, fastguy is actually a pulse of light) the formula comes out to give fastguy moving at speed c relative to both you and slowguy, which makes the statement that you found on the web consistent. 



#8
Feb1413, 01:26 PM

Mentor
P: 28,795

The reason why you think it might move slower is because you are using what we call "Galilean transformation", i.e. the way we add velocities. It has already been shown that this is only valid for velocity that is very much smaller than c, i.e. an approximation. If you start with the postulate of SR, then there is a more generalized way to add velocities. If you are asking WHY c is a constant in all reference frames, we have no answer to that (yet), because that is how Nature behaves as we know it now. Zz. 



#9
Feb1513, 04:54 AM

P: 3,178





#10
Feb1513, 05:16 AM

P: 6

Thank you for you help. 



#11
Feb1513, 06:03 AM

P: 3,178





#12
Feb1513, 06:48 AM

P: 6





#13
Feb1513, 06:57 AM

P: 3,178

v  u  1  uv/c^{2} If you see terms like "tex" and "frac", then there is a problem with your browser or internet reception. 



#14
Feb1513, 08:16 AM

Mentor
P: 11,230

http://hyperphysics.phyastr.gsu.edu...iv/einvel.html There's also Wikipedia, but it probably has more "extra" stuff than you really want: http://en.wikipedia.org/wiki/Velocityaddition_formula As Harrylin noted, your browser isn't decoding LaTeX code for you for some reason. If you're going to hang around here a lot, you really should get that fixed, because we use LaTeX a lot for equations. Try asking about it in "Forum Feedback and Announcements", down at the bottom of the list of forums on our home page. 


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