Sound carries energy
Energy is transferred, not the particles.
A sheet over a container
Fine grains lie on a sheet stretched over a container. A source of sound is switched on some distance away.
What do you think happens to the grains?
What this lesson covers
The idea
Sound is a form of energy: a vibrating source transfers energy to the medium, and vibrations and collisions of its particles carry the energy along; energy is transferred, not the particles.
A sheet over a container
Fine grains lie on a sheet stretched over a container. A source of sound is switched on some distance away.
What do you think happens to the grains?
- They jump about
- They stay still
- They slide towards the source
Sound on, grains jump
Turn the sound on and press Play. Watch the grains.
Energy travels, particles stay
The source gave its energy to the air next to it. That air passed it on, particle by particle, until it reached the sheet. No air particle travelled from the source to the sheet.
Sound is a form of energy. A vibrating source transfers energy to the surrounding medium. The vibrations and collisions of the particles carry the energy along. Energy is transferred, not the particles.
Notes
Sound is a form of energy. A vibrating source gives energy to the medium, and its particles carry the energy along by vibrations and collisions. Energy is transferred, not the particles.
Check yourself
Sound makes the sheet vibrate and the grains move. What does this show?
What does a vibrating source transfer to the medium around it?
How does the energy of sound move through a medium?
- Sound is made of grains. The grains lie on the sheet. They move because the sound carries energy that makes the sheet vibrate.
- Sound is a form of energy — correct. Yes!
- Sound can travel through a sheet but not through air. Sound travelled through the air to reach the sheet. The movement of the grains shows that sound is a form of energy.
- Its own particles, which travel to the listener. In the propagation of a sound wave, it is the energy that is transferred, not the particles of the medium.
- A steady flow of air. Sound is not a flow of air. The source transfers energy to the surrounding medium.
- Energy — correct. Yes!
- By vibrations of the particles and their collisions with other particles — correct. Yes!
- By the particles flowing from the source to the listener. The particles do not travel with the wave. They vibrate, and their collisions carry the energy.
- By the source moving through the medium. The energy is carried by the vibration of the particles of the medium and their collisions.