Sound Energy - Science Lessons for Grade 4 Students
Sound is a form of energy we can hear. We hear sounds using our ears.
How are sounds made?
Take a wooden ruler and place it on your desk so that about 15 cm is over the edge. Hold the ruler against the desk with one hand and flick the other end of the ruler with your other hand.
When you flicked the ruler, a sound was made. Where did the sound come from?
Notice that the ruler moved back-and-forth. The back-and-forth movements are called vibration. Vibrations produce sound. The vibrations travelled through the air and into your ears. You hear the vibrations as sound.
Musical instruments produce sound when parts of the instruments vibrate. The vibrations travel through the air to your ears. In the case of string instruments such as the guitar, when the strings are plucked or strummed, they produce sound.
A drum produces sound when the skin of the drum is hit with a stick or hand. This causes the skin of the drum to vibrate. In the case of a piano, each key is connected to a small wooden hammer. When the key is pressed, the hammer strikes a metal wire. The metal wire vibrates, producing sound. Wind instruments such as trumpets, saxophones and clarinets produce sound when the column of air in the instrument vibrates.
Sound in everyday life
Sound plays an important role in our everyday lives. We use sounds when we communicate with each other. Sounds are used to inform us about the things around us. Emergency vehicles, for example, use sirens to warn that they are nearby.
Telephones, televisions, radios and computers produce sounds. People use sounds to communicate and show their emotions. Animals also make sounds. The sounds they make are used for communication, to warn others of danger, or to help find a mate. Most animals have a highly developed ability to detect dangers and hazards before they affect them, with the help of sounds.
Loudness of sounds
One way that sounds can be different is their loudness. Blowing a whistle, for example, produces a loud sound. A whisper is an example of a soft sound. The loudness of the sound is called its volume. The louder the sound or the higher the volume of the sound, the more energy it has.
How sound travels?
Press your ear against your table and get a friend to gently tap the surface of the table. The sound that you hear is produced when the vibrations travel through the wooden table. So, sound can travel through solids. In the same way, sound can travel through liquids and gases. Did you know that sound travels faster by water, than it does through air? The speed of sound through water is 4 times more than the speed of water through air. However, the speed of water through a metal such as steel is higher than that through both air and water.
(Fun fact: Whales and dolphins use sounds to communicate with one another underwater. However, loud noises from ships can make them deaf!)
How is sound energy measured?
We usually measure the intensity of sound in units called decibels. Decibels (dB) are so named in honor of Alexander Graham Bell, who invented the telephone and the audiometer. An audiometer is an instrument that measures how well a person is able to hear certain sounds.
Why can’t we hear sounds that are produced far from us?
The farther the sound waves move, the more energy they lose. So, we can hear sounds only up to a certain distance. In other words, the greater the distance from the source of a sound, the softer the sound is. Also, it is not as easy to hear sounds on a stormy day as it is on a calm and clear day. The wind and the rainwater make the sound waves lose their energy on stormy days.
Is there any sound in space?
There is nothing existing in space, so there is no medium through which sound waves can move. There is no air in space. For this reason, you cannot hear sounds in space.
What is an echo?
If you are standing in an empty room, and you say something, you can hear yourself repeated. For example, if you say ''Hello,'' a few seconds later, you hear the word ''Hello'' again. This is called an echo. What happens is that the sound waves left your mouth, travelled through the air in the room, hit the hard surfaces of the bare walls, and bounced back again, causing you to hear the sound you just now made.