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Let's learn how sound travels and how humans hear.

Sound is caused by vibrations. These vibrations travel as waves through any medium:

• sound travels best through solids as the particles are so close together
• sound also travels well through liquids where the particles are a bit further apart
• sound travels less well through gases like air where the particles are much more spread out

Most animals (including humans) use some form of sound to communicate with each other, from birds singing, to hippos bellowing, and cats meowing, to children chatting.

Although sound travels very well through solids, most animals communicate using sound waves through liquid (eg. water) or gas (eg. air).

Snakes don't have outer ears like we do. A snake's inner ear is connected to its jaw bone. This is very sensitive to vibrations that travel through the solid ground.

You can also learn how elephants use vibrations across solid earth to communicate, in our guide: How do plants and animals sense touch and vibrations?

Water is a good medium for sound waves to travel through.

For example, whales can communicate through thousands of miles of ocean.

Sound also travels through air.

It doesn't travel as well as it does in gases and liquids but human speech and hearing are adapted for it.

Some people are not able to hear at all. Other people might not hear sounds as clearly, or might not be able to hear as many different sounds.

Sometimes hearing loss is caused by a problem with the ear itself or a problem with the sound-interpreting part of the brain.

People who are deaf, or partially deaf, have a range of tools to help them cope with not being able to hear:

Sign language

Some use sign language, which uses the hands, upper body and facial expressions to communicate.

Others learn to lip read.

Hearing aids

Some people wear hearing aids to amplify sounds.

These tend to be used by people who have some hearing. Some make all sounds louder while others can be programmed to amplify specific sounds that the wearer does not hear very well.

Hearing aids are placed in the ear canal and can be removed by the user.

Cochlear implants

Other people have cochlear implants fitted.

These tend to be used by people who are severely hard of hearing or deaf. The person is operated on to attach the implant. This bypasses the inner ear, picking up sound waves and passing them directly to the nerve leading to the brain.

Hearing aids and cochlear implants don't always work and there can be bad side effects so some people choose not to have them.

Technology is always improving to support people with their hearing.

Many animals have far better hearing than humans!

For example:

• Dogs can hear much higher pitches than humans and can also hear things up to four times further away.

• Bats and owls have also evolved incredibly sensitive hearing to help them hunt in the dark.

To find out more about animal communication check out these guides:

Try this communication experiment!

You will need

• two paper cups with a small hole in each bottom

• a long length of string

• a partner

Sounds travel through solids (like string) more easily than gases (like air). Try making this string telephone and see how well sounds travel through different lengths of string.

Watch this video to find out what to do:

amplify – To increase the volume or make a sound louder.

communication – Sending and receiving information.

medium – A substance that waves can travel through.

particles – The tiny pieces of matter that everything is made up of.

wave – A pattern of motion that transfers energy, such as sound, from one place to another.

Why not test yourself in our fun quiz!