Sound Energy – JSS3 Intermediate Science Lesson Note (Third Term)

Sound energy is a form of energy produced by vibrating objects and carried through a material as a wave.

Behavioural objectives

1. Define sound energy and vibration.
2. Explain how sound is produced and how it travels through solids, liquids and gases.
3. State why sound cannot travel through a vacuum.
4. Describe pitch and loudness and state what each depends on.
5. List the uses and dangers of sound and the ways to reduce noise.

What is sound energy?

Sound is a form of energy that travels through a medium as a wave and is detected by the ear.

• Everyday sign: a loudspeaker shakes when music is playing.
• Everyday sign: you can hear a friend calling from around a corner.
• Noise: very loud or unpleasant sound.

How is sound produced?

Sound is produced when an object vibrates, which means it moves back and forth very quickly.

• Golden Rule: no vibration, no sound.
• Vibration: a rapid back-and-forth movement of an object.

Examples of sound sources

• Human voice: air from the lungs makes the vocal cords in the throat vibrate.
• Guitar: a plucked string vibrates and moves the air around it.
• Drum: the drum skin moves up and down rapidly when it is hit.
• Loudspeaker: its cone vibrates and you can feel it shake when you touch it.

How does sound travel?

Sound travels as a wave through a medium, which is a material such as a gas, a liquid or a solid.

Steps in the travel of sound through air

1. An object vibrates and pushes the air molecules next to it.
2. These molecules push their neighbours, which push the next ones.
3. The vibration passes along the air as a sound wave.
4. The wave reaches the ear and the eardrum vibrates.
5. The brain picks up the signal as sound.

Sound in the three states of matter

• Gases (air): this is how we hear most sounds, but the particles are far apart, so sound travels slowest.
• Liquids (water): sound travels faster than in air. Whales and dolphins use this to communicate over long distances.
• Solids (metal, wood): sound travels fastest because the particles are packed tightly together.

Try this

1. Put your ear on a wooden desk.
2. Ask a friend to tap the other end gently.
3. Notice that the sound is much louder than when it comes through the air.

Can sound travel through a vacuum?

No, sound cannot travel through a vacuum because a vacuum has no particles to carry the vibrations.

• Vacuum: empty space with no matter in it.
• Outer space: there is no air, so an explosion there would be completely silent.

What are the properties of sound?

The two main properties of sound are pitch and loudness.

Pitch

• Pitch: how high or low a sound is.
• Depends on frequency: the number of vibrations in one second.
• Unit of frequency: hertz (Hz).
• High pitch: a bird’s whistle, which has a high frequency.
• Low pitch: a lion’s roar, which has a low frequency.

Loudness

• Loudness: how strong or soft a sound seems to the ear.
• Depends on amplitude: the size of the vibration, which depends on the energy in it.
• Loud sound: a big hit on a drum.
• Soft sound: a tiny tap on a drum.

Difference between pitch and loudness

What is an echo?

An echo is a sound heard again after it bounces off a hard surface.

• Cause: sound waves reflect from surfaces such as walls, cliffs and hills.
• Where heard: large empty halls and open places with a hard wall far away.

What are the uses of sound energy?

Sound energy is used for communication, warning, navigation by animals, medicine and music.

• Communication: speech, singing and phone calls.
• Warning signals: ambulance sirens, fire alarms and school bells tell us something important is happening.
• Animal navigation: bats and dolphins use echolocation. They send out sound waves that bounce off objects, which helps them find their way in the dark or underwater.
• Medicine (ultrasound): doctors use high-frequency sound waves to view babies in the womb and to check internal organs.
• Music: entertainment and cultural celebrations.

Ultrasound is sound with a frequency too high for humans to hear.

What are the dangers of noise?

Noise pollution is harm caused to people by too much loud or unpleasant sound.

• Hearing loss: constant loud noise, such as heavy factory machines or music at full volume in earphones, can permanently damage the tiny hair cells in the ear.
• Stress: constant noise makes people feel annoyed, lose sleep and can raise blood pressure.
• Distraction: loud noise makes it hard for students to concentrate and for drivers to hear signals on the road.

How can we protect ourselves from noise?

We protect ourselves by reducing the noise we make and by blocking the noise we cannot avoid.

1. Lower the volume on earpieces and speakers.
2. Wear earplugs in a very noisy place.
3. Plant trees around buildings, because trees help absorb noise.

Evaluation

1. What do all sound-making objects have in common?
2. Why can we not hear an explosion in outer space?
3. Is sound faster in air or in a metal pipe? Give a reason.
4. State what pitch depends on and what loudness depends on.
5. List three ways of protecting yourself from noise.

Assignment

Draw a table with two columns, “Uses of sound” and “Dangers of sound”. Write three points in each column, with one example of each from your home or school.