Final answer:
The Doppler effect explains the change in wavelength and frequency of waves when the source moves relative to an observer, which results in pitch changes for sound and color shifts for light.
Step-by-step explanation:
The term you are looking for is the Doppler effect, which refers to the change in wavelength (and therefore, frequency) of waves that happens if the source of the waves is moving relative to an observer.
Understanding the Doppler Effect
When a wave source moves, it causes the wave crests to bunch up in the direction of motion and spread out in the opposite direction. For sound waves, this results in a higher-pitched sound (increased frequency) for an observer in front of the moving source and a lower-pitched sound (decreased frequency) for an observer behind the source. In terms of light waves, this leads to a blueshift for a source moving towards the observer and a redshift for a source moving away. This is because the visible light spectrum changes slightly with shifts in wavelength due to the motion of the source.
Applying the Doppler Effect
In astronomy, the Doppler effect is widely used to determine whether celestial objects, like stars or galaxies, are moving towards us (blueshift) or away from us (redshift). The same principle is used in radar guns to measure the speed of a moving car and in medical imaging techniques.
When considering the physics behind this phenomenon, we look at the wave equation: speed of waves = frequency × wavelength. Since the speed of waves remains constant in a given medium, if the wavelength decreases due to movement of the source towards the observer, the frequency must increase and vice versa.