Basics of sound-wave propagation
A Newton's cradle consists of several metal balls of the same size that touch each other and hang from strings. When one ball is lifted and released, it hits the other balls. The motion is passed through the middle balls, and a ball on the opposite side swings outward. Energy is transferred even though the middle balls barely move visibly. The farther the first ball is pulled back, the stronger the transferred motion becomes.
Sound transmission in air works in a similar way. When a sound is produced, air particles begin to vibrate. They push neighboring particles, which then push further particles. In this way, sound spreads through the air. The air particles themselves do not travel across the room; instead, the motion is passed on.
If only one ball is displaced in the Newton's cradle, the transferred motion is smaller—comparable to low sound pressure.
If two or more balls are displaced at the same time, the transferred motion is larger. Likewise, air particles are displaced more strongly, which corresponds to higher sound pressure.
