Sound waves

• Sound travels as longitudinal waves.

  Like this:

  
• The vibrations of the particles are parallel to the direction the wave travels.
• Sound is produced by vibrations.
• Sound waves are longitudinal waves, which means the molecules vibrate back and forth in the same direction as the wave travels.
• Compression is when the molecules are squeezed closer together (higher pressure).

  Like this:

  
• Rarefaction is when the molecules are moved apart (lower pressure).

  Like this:

  
• Sound needs a substance to travel through and travels by vibrating.
• Sound waves travel fastest through dense solids because they have more particles, making it easier for vibrations to pass through.