Sound by 2E1 Shafiatul

What is sound?
Sound is a vibration or a wave of air molecules which is caused by the motion of an object. The density of the molecules is higher when there is a compression wave. This compression wave travels through the air at the speed depending on the temperature of the surroundings. Since a sound wave contain energy which means it can make things move. But, if the sound wave hits something solid, the wave will bounce back forming an echo. Sound cannot travel through a vacuum. It can only travel through solids, liquids, gases and plasmas.

How is sound being produced?
Sound waves
A series of compressions and rarefactions which changes or waves through the air is called a sound wave. Sound waves vibrate at different rates or frequencies as they move through the air. Frequency is measured in cycles per second, or Hertz (Hz). The faster an object vibrates the higher the pitch of the sound. A frequency of 100 Hz means 100 vibrations every second.

Echolocation
The sound which travels to the walls and is reflected back to our ears is called an echo. Echoes are used to find objects underwater, to find large shoals of fish and to measure the depth of the sea. Animals use echoes to find food and to ‘see’ where they are going. For example, bats. They have a poor sense of sight but a good sense of hearing. They use echolocation to find food. Bats produce a high frequency sound to find insects to eat. This sound then reflects off the insect and travel back to the bat’s ears. This helps the bat to find even the smallest insect. Echolocation also helps the bat to ‘see’ where it is flying.

What affects sound?
Sound vibration
When an object moves or vibrates, sound is produced. There could be no sound without movement. When an object moves or vibrates, the air molecules around it will also vibrate. As long as they are not in a vacuum, vibrating objects produce sound. Each molecule moves back and forwards only in a tiny distance which is enough to cause the air particles to bump into each other. This will create areas where there are many molecules pushed closer. This is called compression. Areas where molecules are spread far apart are called rarefactions. Compressions and rarefactions move outwards away from the sound source in circles.

The speed of sound
Sound will take time to travel. In air, sound travels at a speed of 330 metres per second. In fresh water, sound travels at a speed of 150 metres per second. Sound travels at even higher speeds in solids. For example, an iron sound travels at 5000 metres per second. So, the speed of sound depends on density. The denser the material is the faster the speed of sound.

Examples of stuff producing sound
Here are some examples of things that produce sound:
-A guitar
-A trumpet
-A drum
-A bee (buzzing sound caused by its wings)
-A recorder
-Cars
-Airplanes
And many more.

Sources
http://www.sciencetech.technomuses.ca/english/schoolzone/Info_Sound.cfm
Explore your world with Science discovery 2 (pages 202-206)
http://en.wikipedia.org/wiki/Sound