Sound surrounds you, traveling in waves throughout the atmosphere. These waves occur as a result of atoms vibrating and colliding with one another. These vibrations occur from a source and travel throughout the atmosphere -- the vibrations creating waves of energy. Humans and other creatures use these sound waves, not only to communicate but also to perform various tasks.
Without sound waves, human beings could not communicate verbally. Your vocal chords generate sound waves that are then transmitted through the air to the ears of listeners. Modern communication technologies, such as radios and televisions, use this same basic concept to transmit sound to your ears.
Scientists use sound waves in sonar devices when they explore the oceans. Sonar sends out sound waves, which then bounce back to the source when they hit an object. Scientists can use this echo to determine the size and distance of the object that bounced the sound waves back. Navy vessels also use sonar technology to search for enemy submarines.
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Geologists use sound waves to search for resources such as oil under the earth. They bounce sound waves into the ground and measure the way in which they travel through the earth. By measuring the ways in which the sound waves travel through the earth, geologists can make inferences about the density and makeup of the ground. Geologists can also use the waves that earthquakes produce to study the ground in a similar manner, as well as to study the effects and intensity of the earthquakes themselves.
Many creatures use sound waves to hunt for food. Bats especially use a form of sonar to search for prey. Bats project sound waves that bounce off of prey. When the sound waves return back to the bats, they can determine their distance from their prey. In this way, bats can effectively hunt at night despite having relatively poor eyesight. Some sea creatures, such as dolphins, use similar forms of echolocation to both hunt for prey and communicate with one another.