Sound
What is sound and how does it travel?
Characteristics of Sound
What is Sound?
Sound is a form of energy. Sound is caused by vibrating objects and it needs a substance through which to move and a receiver. Sounds can be loud, quiet, soft, or harsh. If you are in a room with loud music, you can feel the vibrations in the air. It can hurt your ears (think of a rock concert). You can also feel the vibrations in the floor, walls, and furniture. We can detect vibrations directly by putting our hand on our throat when we speak or by touching a vibrating tuning fork to the surface of water. Sound vibrations travel through air, wood, metal, water, or any medium. Air is the medium with which we are most familiar and we are able to hear sounds that originate somewhere away from us. We can also put our ears on a table top and hear sounds transmitted from the same source through the wood and the air. Sound travels better and faster in media which are more elastic or more dense. The speed of sound can also be affected by temperature. The higher the temperature of the medium, the faster the speed of sound will be in that medium.
How Does it Travel?
Sound can only travel through a material or medium – it cannot travel through empty space. Outer space is a vacuum. There is no sound in space because there is nothing for vibrations to travel through. You might wonder how astronauts in space can talk with us here on Earth. The sounds astronauts hear are sound waves that have been changed into electromagnetic waves and back again. Electromagnetic waves, like radio waves, can travel through a vacuum like space. Then they are turned back into sound waves. It’s like radio waves traveling to your radio. They are traveling through the air but you can’t hear them. When you turn on your radio, they are changed back into sound waves. The same thing happens when waves travel through space to reach the astronauts. What happens if their helmet radios go on the blink? They can shout until they are hoarse and they still won’t be able to hear one another. There is a very simple backup. They can put their helmets against each other and the vibrations from their voices can pass from one helmet to the other. Portable phones, radios, and walkie-talkies pick up and convert sound waves.
How do Sound Waves Move?
Sound waves move in the same direction as the medium. Think about dominoes lined up. The first domino falls forward and transfers the energy to each domino down the line. You can see the wave move forward as the dominoes fall. Like light, sound waves can be reflected or bounced off an object. When the rock is dropped into the tub, the water in the tub moves outward in a wave. When it hits the sides of the tub, it bounces off and returns. An echo is produced when the initial sound wave bounces back from a surface after a slight delay. Bats are able to capture prey through an echo locating strategy using sound waves. The bat emits a high-pitched sound which travels through the air and hits an insect. The sound bounces off the insect and returns to the bat.
What is frequency?
Different kinds of sounds are made by altered vibrations. The rate of a vibration (or the number of times an object vibrates per second) is the frequency. The frequency determines the pitch (the highness or lowness) of a sound. A fast vibration (shorter wavelength) makes a high pitch tone and a slow vibration (longer wavelength) makes a low pitch tone. A canary’s song is full of high notes while a lion’s roar is made of low notes.