Which surfaces echo?

The idea

Echoes are stronger from hard, smooth surfaces that reflect sound; soft surfaces absorb sound and rough surfaces scatter it, so their echoes are not clearly heard.

Wall, curtain, rocks

You clap in front of a smooth hard wall, then in front of a thick curtain, then in front of a rough wall.

In front of which one do you think you hear the clearest echo?

• The smooth hard wall
• The thick curtain
• The rough wall

Three surfaces

Choose a surface and watch what happens to the incoming sound.

Reflect, absorb, scatter

Echoes are stronger from hard and smooth surfaces that reflect sound. Soft surfaces, such as curtains, tend to absorb sound. Rough surfaces scatter it in different directions. In both cases an echo cannot be heard clearly.

Echoes are stronger from hard, smooth surfaces that reflect sound. Soft surfaces absorb sound and rough surfaces scatter it, so their echoes are not clearly heard.

Notes

Hard, smooth surfaces give stronger echoes. Soft surfaces absorb sound and rough surfaces scatter it, so their echoes are not clearly heard.

Check yourself

Which surface gives a strong echo?

What does a soft surface like a curtain do to sound?

Why is an echo not clearly heard from a rough surface?

You clap in front of a smooth hard wall that is far enough away. How strong is the echo compared with a heavy curtain at the same place?

• A soft surface like a curtain. Soft surfaces tend to absorb sound, so the echo is not clearly heard.
• A hard and smooth surface — correct. Yes!
• A rough surface. Rough surfaces scatter sound in different directions, so the echo is not clearly heard.
• It reflects it strongly. Echoes are stronger from hard and smooth surfaces. Soft surfaces absorb sound.
• It scatters it in different directions. It is rough surfaces that scatter sound in different directions. Soft surfaces absorb it.
• It tends to absorb it — correct. Yes!
• The rough surface scatters the sound in different directions — correct. Yes!
• The rough surface absorbs the sound. It is soft surfaces such as curtains that tend to absorb sound. Rough surfaces scatter it.
• Rough surfaces reflect the sound straight back. Rough surfaces scatter sound in different directions, so the echo is not clearly heard.
• Weaker, because the wall absorbs the sound. Hard, smooth surfaces reflect sound. It is soft surfaces like curtains that absorb it.
• Stronger, because the wall reflects the sound — correct. Yes!
• The same, because both are surfaces. Echoes are stronger from hard and smooth surfaces than from soft surfaces, which absorb sound.