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🧪 Science 💡 Light and sound

Echoes

Echoes can be made by shouting toward a large object at least 9 meters away. The drawing on the far right shows sound waves from a person's voice hitting the side of a big building and bouncing back as echoes. Waves that reach different surfaces return to the speaker at different times, as the drawing on the left shows.
Echoes can be made by shouting toward a large object at least 9 meters away. The drawing on the far right shows sound waves from a person's voice hitting the side of a big building and bouncing back as echoes. Waves that reach different surfaces return to the speaker at different times, as the drawing on the left shows.

📖 In short

An echo is a sound we hear a second time after it bounces off a wall, a mountain or a cave. If you shout “Hello!” in a wide valley between mountains, the sound comes back to you a moment later: “Hello!”, as if someone were answering.

🤩 Did you know?

  • Sound travels through air at about 340 meters per second.
  • In big halls soft materials are put on the walls to soak up sound and stop echoes.
  • Caves and deep valleys are wonderful places to hear echoes.
  • Doctors use the echoes of special sounds to see inside the body.

🔎 Find out more

🌟 How does it happen?

When we shout, sound waves spread through the air in all directions. If they hit a big, hard surface far away, they bounce back to us like a ball off a wall, and we hear them a second time.

🔍 When do we hear it?

We only hear an echo if the surface is far enough away for the returning sound to arrive a little after our own voice. In small rooms the sound bounces back too fast for us to tell it apart.

💡 Animals and echoes

Bats and dolphins use echoes to find their way and their food in the dark or in murky water, making sounds and listening to their echoes.

🎯 Echoes and machines

Ships use sonar, a device that sends a sound to the seabed and measures how long its echo takes to return, so it can tell how deep the sea is and find fish.

🧩 Test yourself

1 What is an echo?

2 Which animal uses echoes in the dark?

3 Sound travels through air at about ?? meters per second.

4 Which picture shows “Echoes”?

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