Understanding Sound Energy

• Sound energy travels through vibrations. When the vibration of the sound's source encounters the particles of what is nearby, compressions and expansions in the air create a wave. The human eardrum moves in response to the sound wave's compressions and expansions. The number of vibrations per second determines the pitch of the sound, and some sounds are too high or low for the human ear to detect.
  
  

Sound Energy and the Paper Cup Telephone

• Speaking into a paper cup telephone transfers vibrations from the speaker's larynx to the air inside her mouth. When the vibrating air connects with the paper cup, the sound energy becomes mechanical energy, or motion, causing the cup to vibrate. Vibrations in the speaker's cup travel through the string connecting the two cups, causing the receiver's cup to vibrate. When the air inside the receiver's cup vibrates, the mechanical energy becomes sound energy again and can be detected by the receiver's eardrum.
  
  

Where Does Sound Energy Go?

• After the sound waves are detected by the receiver's eardrum and heard, the sound energy does not stop. It will continue moving forever unless the sound energy is converted to another form of energy. As sound waves travel outward, particles transfer their mechanical energy as they collide. Some particles may fail to transfer all of the mechanical energy, reserving it instead for internal heat energy.
  
  

Factors in Sound Travel

• If the string of a paper cup telephone is not held taut, the sound energy will not successfully travel through the string. Because sound travels by vibrating particles colliding, the closer particles are to one another, the more quickly the sound wave will travel. Sound energy can be absorbed by soft, rough materials, such as carpet, or reflected to create an echo by hard, smooth materials.