Physlet Illustration: The Doppler Effect for a Moving Observer

 

 
F = m/s
A fixed source emits spherical wave fronts once each second (f  = 1.0 Hz) as shown. The waves move outward with a speed of 1.0 m/s.  An observer in a red ship moves, first toward the source and then away, with a constant speed that you control (between 1.0 and 10.0 m/s).  What is the frequency observed on approach and when receding? Does it depend upon the speed of the observer?

Hints

  1. Pause the simulation when the ship approaches the outermost wave front and single step forward.  Measure the time period, T,  between wave front crossings and invert this period to find the observed frequency, f = 1/T. 
  2. Measure the observed frequency when the ship is receding and compare to that when approaching. Is it higher or lower?

Reference

See Walker, Section 14-6

Illustration written by Chuck Niederriter