Final answer:
The Doppler effect is readily observed with sound on Earth due to relatively significant speeds compared to the speed of sound, but not with light due to light's extremely high speed. Nonetheless, Doppler shifts for light are key in astrophysics for measuring stellar and galactic velocities.
Step-by-step explanation:
The question relates to understanding why the Doppler effect can easily be observed with sound waves on Earth but is not commonly observed with light waves. The Doppler effect occurs when there is relative motion between an observer and a wave source, such as sound, light, or water waves. With sound, this effect is noticeable on Earth because the speeds involved, such as a speeding ambulance, are significant compared to the speed of sound. However, with light, the effect is not commonly observed because the speed of light is so extreme that everyday speeds on Earth are insufficient to produce a noticeable Doppler shift in the frequency of light. Nevertheless, the Doppler shift for light is observable in astronomical contexts, such as determining the velocities of stars and galaxies, which move at significant fractions of the speed of light relative to us. These shifts in the frequency of light received from the cosmos have greatly contributed to our understanding of the universe.
Doppler shifts can be used in determining velocities in various scenarios, such as when ultrasound waves are reflected from blood for medical diagnostics, or in studying the recession of galaxies. The effect is produced by radial velocity – motion that is directly toward or away from the observer. The Doppler shift does not occur with motion that is perpendicular to the line of sight, and hence sideways motion does not produce a noticeable effect on the frequency of light or sound as observed by the person or the instrument.