Sound is a pressure wave, but this wave behaves slightly differently through air as compared to water. Water is denser than air, so it takes more energy to generate a wave, but once a wave has started, it will travel faster than it would do in air.
A relay race
Sound travels by particles bumping into each other as they vibrate. It is a little like a relay race – each runner holds a little bit of information (the baton), and when they make contact with the next runner, they pass the information on.
In the case of sound, the runners are particles and the information (baton) they are passing along is energy of vibration. In a sound wave, a particle picks up some energy and keeps it until it bumps into a neighbouring particle. The next particle will then pick up the energy and transfer it to the next one in the chain. This happens extremely fast and is detected as a wave of pressure.
Sound won’t travel in a vacuum because there are no particles to bump together to transmit the vibration.
Sound in air
In a gas like air, the particles are generally far apart so they travel further before they bump into one another. There is not much resistance to movement so it doesn’t take much to start a wave, but it won’t travel as fast.
Sound in water
In water, the particles are much closer together, and they can quickly transmit vibration energy from one particle to the next. This means that the sound wave travels over four times faster than it would in air, but it takes a lot of energy to start the vibration. A faint sound in air wouldn’t be transmitted in water as the wave wouldn’t have enough energy to force the water particles to move.
Sound in solids
In a solid, the particles are even closer together and linked by chemical bonds so the wave travels even faster than it does in either liquid or air, but you need quite a lot of energy to start the wave at the beginning.
Sound and temperature
Temperature has a marked influence on the speed of sound. This is not due to a change in how closely together the particles are to each other but relates to the amount of energy that each particle has. Hot particles have more energy and transmit sound better than cold particles. Water in Antarctica will transmit sound slower than water in the tropics.
Some comparisons for the speed of sound in different materials
| Air at 20°C | 343 metres per second (m/s) – also known as Mach1 |
| Air at 0°C | 331 m/s |
| Helium at 0°C | 965 m/s |
| Water at 20°C | 1,482 m/s |
| Water at 0°C | 1,417 m/s |
| Solid steel | 5,960 m/s |
Related content
Explore the science concept related to sound further with these articles:
- Hearing sound – the basics of sound waves
- Measuring sound – the different parts of a sound wave, how we talk about and measure sound
- Sound – visualising sound waves – helps students to 'see’ sound waves with videos and diagrams
In our recorded PLD session Sounds of Aotearoa a group of primary science educators introduce some fun ways you can learn and teach about sound.
Activity ideas
Use these activities to explore some essential physics ideas relating to sound, but in a whole new way.
- Modelling waves with slinkies – stay indoors and model how sound travels.
- Catching worms using ground sounds – go outdoors and investigate whether there is any evidence that earthworms respond to vibrations in the ground.
- Sound detectives – can you locate sounds while blindfolded?
- Make and use a hydrophone – and listen to underwater sounds.
- Sound on an oscilloscope – use oscilloscope software and your computer to make and watch a visual sound display.
- Investigating sound – simple exploratory activities and questions to experience and build an understanding of sound.
- Hearing sounds – using whispers and vibrations to hear and experience how sound moves.
- Hearing sounds under water – go underwater yourselves to listen to sounds
- Measuring the speed of sound – use a timing app to measure the speed of sound.
