The following active reading exercise includes a short test and tasks suitable for students aged 11 to 14 when studying waves and sound.

When waves hit a surface, they are reflected. This means they bounce off the surface and come back. For example, light is reflected by the surface of a mirror.

When you are high up in the mountains and call out in a loud voice. Your sound waves will be reflected by a mountain surface nearby and you can hear it coming back after a few seconds. This is called an echo.

You can measure the distance from where you stand to the mountain surface and time how long it takes until your hear the echo. With this information you can calculate the speed of sound.

This principle is used by animals like dolphins and bats for navigation. They send out sound waves and listen for their echo. This helps them to work out how far away predators or food are. When used like this echoes are called sonar.

Sonar is also used by submarines for navigation. Submarines send our sound waves and listen for the echo to know their own position. They can also detect other submarines and ships.

Tasks:

1. Box the words in the text you do not know.
2. Highlight what happens to waves when they hit a surface.
3. Highlight the word that describes the reflection of sound waves.
4. Circle the two types of waves that are mentioned in the text.
5. a) Underline the animals that use sonar.
6. b) Underline how submarines use sonar.

*Extension: Explain what a dolphin needs to know to work out the distance to a fish when using sonar.