Waves are a means by which energy travels. There are physical waves such as sound and water waves. There are also electromagnetic waves such as light waves. Diffraction is the bending of waves as they pass through an opening or around a barrier in their path. We can hear around a corner because of the diffraction of sound waves. Reflection is the change in direction of waves when they bounce off a barrier. Refraction is the change in direction of waves as they pass from one medium to another.