Physics
Doppler effect
Moving source and observer, wavefronts and the Mach cone.
What happens
A moving source drags its wavefronts into crowded circles ahead and stretched ones behind: higher pitch approaching, lower receding. Drag the green observer anywhere and read the received frequency live; push the source past the wave speed and the circles fold into the Mach cone of a sonic boom.
Try this
On approach f′ = f / (1 − v/c): 1.5 means v = c/3, not c/2 - that is the receding formula turned round.
Equations used in the module
Equations f′ = f(c+v_o)/(c−v_s) sin θ_M = c/v_s; v_s > c
