How loud it is

A clay pot struck gently sounds soft. Struck hard, the same pot sounds loud.

The dashed line marks the resting level. A crest is the highest point of a wave on a graph.

Rule

A bigger amplitude means a louder sound and more energy. Loudness does not change how fast the sound travels.

• Amplitude — the biggest change from the resting level. On a graph, it is a crest's height above the dashed line.
• Intensity — the sound energy crossing one unit of area each second.

A harder hit puts more energy into the pot. The wave has a bigger amplitude. You hear a louder sound.

Far from the source, the same energy spreads over a bigger area. So the intensity falls. The sound seems softer.

Loudness is measured in decibels (dB). Ordinary talk is about 60 dB.