Sound is a sensation or feeling that we hear. We produce sounds by doing something. The motion of materials or objects causes vibrations. A sound originates in the vibration of an object, which makes the air or another substance around the object vibrate. The vibration of the air moves outward in all directions in the form of a wave.5 The following are examples of how certain sounds are produced.
The human voice is produced in the larynx, which is a part of the throat. There are two small pieces of tissue that stretch across the larynx with a small opening between them, these tissues are our vocal cords. As we speak, muscles in our larynx tighten the vocal cords making this small opening become narrower. When air from our lungs passes through the tightened cords a vibration is produced. This vibration produces vocal sounds. The tighter the vocal cords, the more rapidly the vocal cords vibrate and the higher the sounds that are produced. This is what causes the human voices to have different pitches.6
Animals also produce sounds. Almost all mammals, birds, and frogs have vocal cords or similar structures, which allow them to produce sounds in a similar way to humans. However, many other animals produce distinctly different sounds. For example, bees buzz as they fly because of the rapid movement of their wings. Their wings make the air vibrate producing a buzzing sound. A cricket produces a singing type sound as it scrapes parts of its front wings together. Some types of shellfish produce clicks by tapping their claws together.7
Musical instruments produce many different sounds in various ways. There are three categories of musical instruments, percussion, string, and wind. Some instruments need to be struck by an object in order to produce a sound, these are called percussion instruments. For example when the membrane of a drum is hit the membrane vibrates, producing a sound, or when a bar of a xylophone is struck, a sound is produced. Each bar of a xylophone produces a different note when struck. String instruments, such as a harp or violin, produce sounds when one or more of their strings are plucked, causing them to vibrate. This vibration causes parts of the body of the instrument to vibrate, creating sound waves in the air. The pitch of a stringed instrument depends upon the string's thickness, its length, the distance stretched, and the number of times it vibrates. Wind instruments, such as a flute or trumpet produce sound when a column of air inside the instrument vibrate. For example, with a trumpet it is the vibrating lips of the player which makes the air column vibrate.8 Sounds produced by musical instruments are usually pleasing for us to hear. "A musical sound is a regular vibration." 9
Humans, animals, and instruments are not the only sounds we hear, many of us come across various other sounds or noise every day. For example thunder is caused when lightning heats the air, causing the air to vibrate. A car makes a rather loud noise, which is produced when the engine vibrates, causing the other parts of the car to vibrate.10 These types of noises are produced by irregular vibrations occurring at irregular intervals. This is what makes noise a rather unpleasant sound.11