Modern Physics Problem 10.1.2: Reference Frames

Select a relative velocity, v/c:


A moving red rectangle simulates a space ship passing directly over another space ship, a green rectangle. A light flash occurs when the left sides coincide and again when the right sides coincide.


Two measuring sticks pass close by each other with relative speeds comparable to the speed of light.  A light flash occurs when the right ends of the sticks coincide, event 1, and again when the left ends coincide, event 2.  Which of the following is true for all relative velocities?  You can view the events in either the green reference frame or the red reference frame.

  1. There is a unique speed when the events are simultaneous in both reference frames.
  2. Event 1 always occurs before event 2.
  3. At a given speed, both the red and green observers will always agree on which event occurred first.
  4. None of the above.


See Giancoli-PA 26-4.


None of the above.


Physlet problem authored by Wolfgang Christian.