These, friends, are sound waves. It's important to remember that sound waves are compression waves. Sound waves are not like the waves on the ocean or the waves you get by waving a stretched-out rope. Frequency and pitch Sound waves have a frequency , which is the number of compression pulses that go past a fixed point in a given amount of time. The frequency of audible sound is measured in hertz, or cycles per second.
Sound waves have a wavelength , which is the physical distance between compression pulses.
The wavelength is inversely proportional to the frequency. You perceive the amplitude of the wave as loudness. Unless you hold the tuning fork right next to your ear, you won't hear much of anything. This is because a small tuning fork can't push very much air around. Now take the same tuning fork, whack it on your knee again, and touch the non-forked end to a tabletop or other handy wooden surface.