Examples of sound energy include sounds made by singing, whistling, musical instruments and horns. Sound is a vibration that causes a wave of pressure through air, water, wood and other mediums. It is heard when the wave reaches the ear and is perceived by the brain. Sound waves have characteristics including their frequency, amplitude, intensity, speed, direction and wavelength.
Receipt of sound by any living creature that can hear is limited to certain frequencies. Humans can hear sounds between 20 hertz and 20,000 hertz. Low and high limits of hearing decrease as someone gets older. Species other than humans hear differently. Dogs can hear sounds higher than 20,000 hertz but cannot hear sounds below 40 hertz. Many animals use sound for navigating, communicating and perceiving danger. Species including birds, frogs and certain mammals have special organs that produce songs and other sounds. Noise refers to sound that is unwanted or is a nuisance.
Other types of energy exist in addition to sound. Radiant energy is heat and light that travels in waves in all directions. The sun and the hot coils in an electric heater are examples of radiant energy sources. Atomic energy is produced when atoms are split, such as in nuclear power plants and atomic bombs. Mechanical energy is produced by all moving objects, such as cars, bicycles and people. Chemical energy is stored in potential fuels, such as gasoline, food or combinations of chemicals. Moving electrons produce electrical energy, which occurs in batteries, motors and electrical outlets.