2.2 Sound
Summary: If you very gently press the front of your throat while you are talking, you will feel a vibration. This is your vocal cords vibrating. These vibrations produce the sound waves that travel through… Tags: science oxford-science student-book-7 physics Created: 2026-05-19 Last Updated: 2026-05-19
After this topic, you will be able to:
Think back
- What type of wave is a sound wave?
- What must an object do to produce a sound wave?
- What can sound waves travel through?
Key idea Sound must travel through a medium (a solid, liquid, or gas). The speed of sound is slower than the speed of Light.
Key words medium, vacuum, speed of sound, speed of light
If you very gently press the front of your throat while you are talking, you will feel a vibration. This is your vocal cords vibrating. These vibrations produce the sound waves that travel through the air from your mouth when you speak.
What is a sound wave?
All speakers, including the ones inside headphones, have a part that moves backwards and forwards. This part vibrates or oscillates, which makes the air Molecules close by move backwards and forwards. This vibration produces a sound wave, as you can see in Figure 1. Some people think that sound just ‘dies away’. This is not true. It spreads out as it moves away from the source.
Figure 1Sound is caused by vibrations, such as the vibrations at the ends of a tuning fork, which move air molecules – and even water molecules – backwards and forwards. Full text alternative to the content
A Name an object in your home that produces sound when it vibrates.
What does sound travel through?
The dolphins you see in Figure 2 and whales use sound waves to communicate underwater. Elephants stamp their feet when a lion comes near them. This warning sound travels through the ground to other elephants. Sound needs a medium like a solid, liquid, or gas to travel through. It cannot travel through empty space (known as a vacuum) because there are no particles to vibrate.
Figure 2Dolphins communicate underwater.
How fast does sound travel?
The speed of sound in a medium depends on the arrangement of particles in that medium. Table 1 shows the speed of sound in different types of medium. The particle arrangements help us to explain the different speeds of sound. For example, the particles in a solid are very close together, so vibrations are passed along more quickly than in a gas. Table 1 The speed of sound in different types of medium. State
solid
liquid
gas
Particle arrangement
Speed of sound (example)
5000 m/s in steel
1500 m/s in water
340 m/s in air
B The speed of sound in a substance is 4000 m/s. Suggest whether the substance is a solid, liquid, or gas.
People sometimes talk about the ‘sound barrier’. There is no difference between travelling at the speed of sound or faster than it. Chuck Yeager found this out in 1947. He became the first human to travel faster than the speed of sound in an aircraft. Figure 3 shows Felix Baumgartner, who was the first person to travel faster than the speed of sound in free fall. He jumped from a balloon 24 miles above the surface of Earth. There is very little air at that height.
Figure 3Felix Baumgartner travelled faster than sound.
C When Felix jumped, his speed increased very quickly. Suggest why this happened.
Which is faster: sound or light?
Light travels much faster than sound. The speed of light is 300 000 000 (300 million) m/s. This is almost one million times faster than sound. You can notice this difference during a thunderstorm. Thunder and lightning are produced at the same time. You see the lightning almost immediately. However, it takes a longer time for the sound of thunder to reach you. Light can also travel through a vacuum. This is because it does not need a medium to travel through.
Maths skills A girl sees a flash of lightning and then hears the thunder four seconds later. a) How far away is the storm? Give your answer in km. b) What would she notice when the storm is directly overhead?
Stretch zone
- Copy and complete the sentences. Sound is produced by objects that vibrate/wave. This makes the air molecules melt/move and produces a sound wave. Sound travels fastest in gases/solids and slowest in gases/solids. Sound cannot travel through a liquid/vacuum.
- Explain why sound travels slower in a gas than in a liquid.
Stretch zone
- Compare the amount of time it would take light to travel 10 m from your teacher to your eye with the time it would take sound to travel the same distance.