Uses of sound

Sound plays an important role in our lives. We use sound to communicate in the form of speech, music and noise. Many animals use sound to communicate as well! But it’s important to know that sound is so much more than what we can hear. Sound is produced when an object vibrates, causing particles of the medium surrounding the object to vibrate as well.

This medium could be gas, liquid or solid. These vibrations of particles travel through the medium in the form of a sound wave. As the sound wave travels from the source, it creates areas of higher pressure - compressions - and lower pressure — rarefactions — in the medium. The number of times this pattern repeats every second is the frequency of a sound wave, which is measured in hertz. And while the human ear can detect sounds with frequencies between 20 and 20 000 hertz, sound waves can actually range from one to more than one million hertz!

Sound waves with frequencies below 20 hertz, are called infrasonic waves or infrasound. Some animals, such as whales or elephants, use infrasound to communicate over vast distances — sometimes hundreds of kilometres. Scientists use infrasound to detect earthquakes and volcanic eruptions. Infrasound can even be used to map things underground, such as rock formations! What about sound waves with frequencies above the threshold of human hearing?

Sound waves with frequencies above 20 000 hertz produce ultrasound. Some animals, including bats, use ultrasound waves. But interestingly, bats do not use ultrasound to communicate. Instead, bats use ultrasound to locate their next meal! Bats are mostly active at night and can’t see their prey easily.

So instead of relying on their eyes, bats emit ultrasound waves which travel through air until they reach objects, for example, trees they should avoid flying into or tasty flying insects. The ultrasound waves get reflected from the prey, similar to an echo. Depending on how long it takes for the reflected ultrasound to reach the bat, the bat can locate its prey precisely. This is echolocation. While humans can’t use echolocation, scientists have developed instruments that can use echolocation to locate objects underwater.

These instruments are known as sonars. Sonars use a mechanism similar to bat echolocation — they send out ultrasound waves and detect the echos to tell where an object is. This technology was initially developed during World War I to detect enemy submarines, but has since been used by fishermen, archaeologists, and scientists, for example, those who study the ocean floor. Ultrasound has many uses in medicine as well. One of the most well-known medical uses of ultrasound is for following the developing fetus during pregnancy.

In this case, a machine, quite similar to the sonar, is used to send ultrasound waves into the human body. The same machine, then also records the reflected waves from inside the body, and forms a picture on the screen. The ultrasound scanner can also be used to examine different organs, such as kidneys, ovaries, and the uterus. Ultrasound can help treat some medical conditions too! For example, vibrations of high-intensity ultrasound can precisely target kidney stones, and safely break them up.

Whether in hospital or on a fishing boat, sound has many uses beyond communication. Learning about different types of sound can help us find even more useful applications!