Strike harder, more energy

The idea

A wave with larger amplitude carries more energy; striking a source harder transfers more energy to the medium, giving larger particle displacements and a larger amplitude.

Gentle and hard

Anil strikes a drum gently, then hard. He uses the same drum each time.

What do you think changes when the drum is struck harder?

• The wave has a larger amplitude and carries more energy
• The wave has a smaller amplitude
• The wave carries the same energy

Strike it harder

Slide to strike the source harder. Watch the wave and the two bars.

Bigger wave, more energy

A harder strike gives more energy to the particles of the medium, so they move farther from their mean positions. The wave has a larger amplitude. In the sheet experiment, the grains jump higher.

A wave with a larger amplitude carries more energy. Striking a source harder transfers more energy to the medium, giving larger displacements of its particles and a larger amplitude.

Notes

A larger amplitude means more energy. Striking a source harder gives the medium more energy and larger displacements.

Check yourself

Which wave carries more energy?

A source is struck harder. What happens to the energy transferred to the surrounding medium?

In the sheet experiment the source is struck harder. What do the grains do?

Striking a source harder gives the particles of the medium...

• The wave with the smaller amplitude. A wave with a larger amplitude carries more energy than one with a smaller amplitude.
• The wave with the larger amplitude — correct. Yes!
• They carry the same energy whatever their amplitudes. The amplitude and the energy a wave carries are related. A larger amplitude carries more energy.
• Less energy is transferred. When a sound source is struck harder, more energy is transferred to the particles of the surrounding medium.
• The same energy is transferred. Striking harder transfers more energy to the surrounding medium.
• More energy is transferred — correct. Yes!
• They jump higher — correct. Yes!
• They jump less high. More energy reaches the sheet, so it vibrates to a larger displacement and the grains jump higher.
• They stay at rest. The sheet still vibrates, and with more energy it vibrates to a larger displacement.
• Smaller displacements from their mean positions. More energy causes larger displacements from the mean positions.
• Larger displacements from their mean positions — correct. Yes!
• A permanent move away from their mean positions. The particles still vibrate about their mean positions. They do not travel with the wave.