Sound

Sound is longitudinal wave. The frequency of the wave is heard as pitch, with higher frequencies corresponding to higher pitch. The amplitude of the wave is heard as volume, with larger amplitudes corresponding to louder sounds.

Beats occur when waves of similar frequency interfere with one another. The frequency of the beats you hear equals the difference between the source frequencies.

Resonance occurs when an object oscillates at its natural frequency. Standing wave patterns occur during resonance. These patterns help to determine the notes that musical instruments make.

The Doppler Effect occurs when a source of sound is moving relative to a observer. When the source and observer are moving towards each other, a higher frequency is perceived, and when the source and observer are moving away from each other, a lower frequency is perceived. When the source of sound is moving quicker than the speed of sound, a sonic boom may be heard as a combined pressure wave reaches the observer all at once.