Question

The change in pitch of a train's horn as it passes while you are standing still can be explained by

A. ultrasonic vibrations.
B. resonance.
C. the Doppler effect.
D. sympathetic vibration.

Answer 1

The correct answer is C. the Doppler effect.

Simply put, the Doppler effect is hearing the sound become louder as it approaches you, then reaching the highest possible loudness when its in front of you, and then slowly losing its volume as it leaves you. This of course is not the scientific explanation, but is good for understanding the basic concept of the Doppler effect.