Question

As you sit outside, the sound of a siren becomes lower in pitch. Is the emergency vehicle moving away from or towards you? explain how you know

Answer 1

The sound you hear as the siren gets closer will increase in pitch and that will decrease as it moves away from you.

Explanation:
Sound is a longitudinal pressure wave. As the ambulance moves closer to you, the air molecules get compressed together. The wavelength of the sound (these pressure waves) decreases, and the frequency increases. That results in a higher sound pitch.