This is called the Doppler effect. A sound-producing object coming closer will sound louder than a sound-producing object moving away. The speed of this moving object effects how much this is noticeable.
See link in the discussion area.
Doppler Effect
Whenever the frequency of a sound wave changes, regardless of what caused it to change, the change is perceived as a change in the pitch of the sound.
Every sound vibrates with a particular fundamental frequency. When you change the wavelength of a sound, you change the pitch of a sound.
You have to amplify the sound.
The so-called pitch of the sound would change. A sound with a higher frequency is said to have a higher pitch.
Change the frequency.
Change the frequency.
When the frequency of the vibrations that produce the sound change. Higher frequencies -> higher pitch. OR if the source of the sound is moving towards or away from you -> Doppler effect.
In sounds with higher pitches, the compressions that make up the sound are closer together; when the pitch is lower, they are farther apart. The wavelength of a sound, which is the distance from one compression to the next, is the speed of sound divided by the sound's frequency (pitch).
The frequency of the vibrations. Sound frequencies are directly related to the perceived pitch.
The Doppler effect.The Doppler effect.The Doppler effect.The Doppler effect.
To make sound frequency change alter the pitch.