When a sound source approaches you, how does the pitch change?

The pitch increases

Explanation:

This effect is called Doppler effect. Doppler effect occurs when the source of a wave (such as a sound wave) moves relative to a stationary observer. In particular, two situations can occur:

- When the sound source moves towards the observer, there is a decrease in the apparent wavelength as seen from the observer; since frequency is inversely proportional to wavelength, the observer hears a sound with apparent higher frequency, which corresponds to a higher-pitch sound.

- When the sound source moves away from the observer, there is an increase in the apparent wavelength as seen from the observer; since frequency is inversely proportional to wavelength, the observer hears a sound with apparent lower frequency, which corresponds to a lower-pitch sound.

In this case, the sound source is approaching you: so we are in the 1st situation, therefore the pitch of the sound increases.