1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Relativity and the speed of light

  1. May 12, 2013 #1
    It is a general question just to boost my understanding

    With a stationary boat both observers hear the horn at the same time as they are the same distance away from the horn.

    In the bottom picture of the three pictures above:
    If I make the boat move forward through the air at one block per time interval to the right, (the air is the medium the sound wave travels through). The observers are still the same distance away from the horn. The sound waves travel at two blocks per time interval in both directions.

    So person 1 hears the sound in one time interval and person 2 hears the sound in 3 time intervals.

    Is this above logic sound, (sorry)


    But with light both observers see the light at the same time and record the same speed for the light wave as it has travelled the same distance to each in the same time interval.

    Hope this all makes sense.
    Is this logic so far correct.
    Last edited: May 12, 2013
  2. jcsd
  3. May 12, 2013 #2


    User Avatar

    Staff: Mentor

    Your explanation for the sound is coorect

    Yes. The two observers and the source are all in the same inertial frame, so there is nothing special whether the boat is moving or not.

    They will always measure the same speed of light: it is the one thing that is constant for all observers.

    And there is no such thing as the ether...
  4. May 12, 2013 #3
    So this situation is ok for explaining that the light waves are not propagating through any medium. So no ether. I suppose I need to go off next and think about the Michelsom Morley experiment. If I understand correctly that experiment was set up to look for the ether. Thanks for your help Dr Claude
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted