There is sound all around us all the time, even when we think there is silence there may be sounds out of the human range of hearing. What exactly is sound? Physicists have been studying sound for as long as recorded history. Over 2,000 years ago, Greek philosophers recorded their thoughts on sound and the theory of sound waves. As time went on, we learned more and more about the science of sound and how it works.

Sound is made by vibrations. A vibration is the repeated back and forth motion of an object. These vibrations are called sound waves. We can’t see the waves that sounds make because we can not see air molecules moving.  Although every animal has the ability to hear and make sound, each one is different.

Some sounds can not be heard by humans. This is because of the frequency of the waves or how close together the waves are. There is a term called Hertz(hz) that is used to measure the frequency of sound. The closer these waves are to each other, the higher the pitch. A dog can hear high pitched sounds that a human can not, while elephants and whales are able to hear much lower pitched sounds than we do. This is mainly because of the size of the bones in our ears. The smaller the bone is, the easier it vibrates making high sounds easier to hear. The opposite is true for bigger bones.

Sometimes you will hear someone talking about the speed of sound. This is basically how fast the sound waves are moving through a medium. A medium just means air, water, rocks and that kind of stuff. The more solid something is, the faster sound travels through it, and sound is pretty fast. Sound can move as fast as 761 miles per hour through air, or 1,236 kilometers per hour. The official name for the speed of sound is Mach1.

When something like an airplane travels faster than 761 miles per hour, it has broken the sound barrier. When this happens directly above you, you may hear the sound of air being compressed very quickly. That is called a sonic boom. Planes that can fly faster than the speed of sound are called supersonic. The first supersonic airplane was the Bell X-1. It was flown by Air Force Captain Charles E. (Chuck) Yeager. If something is Hypersonic, it is moving five times the speed of sound.

Have you noticed that when it snows the world seems quieter? This is because the snow actually absorbs sound waves.