Question

a fire truck siren siren getting louder as it braces towards you and quieter as it moves away is called

Answer 1

Doppler effect.

Step-by-step explanation:

Of course, to an observer on the truck, the pitch does not change at all.

Answer 2

As distance from the sound source increases, the area covered by the sound waves increases. The same amount of energy is spread over a greater area, so the intensity and loudness of the sound is less. This explains why even loud sounds fade away as you move farther from the source