Science
What is sound and how does it travel?
Quick answer
Sound is made when something vibrates. The vibrations travel through air, water or solids to our ears. Sound cannot travel through empty space.
In one sentence
Sound is a kind of energy made when something vibrates, and the vibrations travel through the air (or other materials) into our ears.
Explained
Pluck a rubber band and watch it blur back and forth. That fast shaking is a vibration, and it makes a sound. Every sound begins with a vibration: a drum skin, a guitar string, your vocal cords when you speak.
The vibrating object pushes on the air particles next to it. They bump into the next particles, which bump into the next, passing the vibration along like a Mexican wave in a stadium. When the vibrations reach your ear, your eardrum vibrates too, and your brain hears a sound. Find out more in the senses.
Sound needs something to travel through. It travels through gases like air, liquids like water and solids like wood or metal. In fact, it travels faster in water and solids than in air. In space, there is almost nothing to carry vibrations, so space is silent.
In air, sound travels at roughly 340 metres per second. That's fast, but light is nearly a million times faster. That's why you see lightning before you hear thunder. Count the seconds between the flash and the rumble and divide by 3 to estimate the distance in kilometres.
Sounds differ in two main ways:
- Volume (loud or quiet) depends on how big the vibrations are. Hit a drum harder for a louder sound.
- Pitch (high or low) depends on how fast the vibrations are. Short, tight or thin things vibrate faster and make higher notes.
Examples
| Instrument | What vibrates | How to change pitch |
|---|---|---|
| Guitar | strings | press strings to make them shorter |
| Drum | skin | tighten the skin |
| Recorder | air inside the tube | cover holes |
| Xylophone | wooden or metal bars | shorter bars make higher notes |
drum
guitar
xylophone
trumpet
Common mistakes
- "Sound can travel through space." Films add sound effects, but real space is silent.
- "Loud sounds are high and quiet sounds are low." Volume and pitch are different. A tuba can play a loud low note.
- "Sound travels faster in air than water." It is about four times faster in water.
Quick quiz
Sound
Check what you know with 4 quick questions.
Question 1 of 4
What makes all sounds?
Practise it
Try it
Make a string telephone with two paper cups and see how sound travels along a tight string. Then try more physics activities.
Sound and physics activities
For grown-ups
Related topics
The senses
The five main senses are sight, hearing, smell, taste and touch. Sense organs such as the eyes, ears, nose, tongue and skin collect information and send it to your brain.
Light
Light is a form of energy that travels in straight lines, very fast. We see things when light from them enters our eyes, either because they make light or because they reflect it.
Forces
A force is a push or a pull. Forces can make things start moving, speed up, slow down, change direction or change shape. They are measured in newtons.
Electric circuits
An electric circuit is a complete loop that electricity flows around. A simple circuit has a battery, wires and a component like a bulb. If the loop is broken, the electricity stops.
Electricity
Electricity is the flow of tiny charged particles called electrons through a material. It powers lights, phones and machines, and it can come from batteries or the mains supply.
Friction
Friction is a force that acts when two surfaces rub or slide against each other. It slows things down and turns movement into heat, and it also stops us slipping.