Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Relative motion, frames

  1. Nov 20, 2009 #1


    User Avatar

    So, for example, 2 objects are moving towards each other.
    There is a frame where 2 object move with (for the sake of simplicity thy both move with the same velocity) the velocity V
    Then there is a frame where one of the object stand still, but the other moves towards it with the velocity 2V.
    That makes sense, it's what relativity is all about.

    But the tricky part comes when the objects moving towards each other have the velocity, for example, 70% c
    There is a frame where each one moves with 70% c (?)
    There is a frame where one object stands still while other object moves with the velocity of 2*70% c = 140%c (??)

    Clearly something is wrong with this, but I just can't put my finger on it...
    Please teach me! ;)
  2. jcsd
  3. Nov 20, 2009 #2


    User Avatar

    Staff: Mentor

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook