Humans and many animals can produce sound and use it to communicate. Many objects can also produce sound when hit or rubbed against each other. Sound produced by objects can also be used to identify the type of material used in production of that object. For example if you see a clear jar and you are wondering if it is plastic or glass, you nock on it and listen to it's sound. Sound has many medical and industrial applications as well. Sound is used in the sea to locate and identify submarines, fishes and under water elevations. It is also being used see inside the human body.