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Unit 6: Sound and space

Reflections of sound — HIA International - Grade 8 Revision Notes & Topical Questions

5 min read 8 parts Lesson 3 of 14 2 quizzes

📚 HIA International - Grade 8 Hub / Topical Revision
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Lesson summary

Reflections of sound — HIA INTERNATIONAL notes: Explain how sound is reflected, what echoes are and how echoes are used or avoided.Reflection — all waves can be reflected, so sound waves can be reflected from surfaces.Like a ball — a wave comes back off a wall like a bouncing bal…

  • Best surfaces
  • Poor surfaces
  • Calculation
  • Recording studios
  • Surface comparison
  • Limitation

Part 1 of 6Reflection of sound

Reflection
  • Reflection all waves can be reflected, so sound waves can be reflected from surfaces.
Like a ball
  • Like a ball a wave comes back off a wall like a bouncing ball, but is not affected by gravity.
Best surfaces
  • Best surfaces large, smooth, flat surfaces such as glass, tiles, flat metal and smooth concrete.
Poor surfaces
  • Poor surfaces soft materials such as curtains, thick carpet and blankets absorb sound.

Part 2 of 6Echoes

Echo
Echo the reflection of a sound wave.
Clapping
  • Clapping a clap between two flat walls seems to last longer and fade away because of the reflections.
Distance
  • Distance the sound travels to the surface and back, so it covers double the distance to the surface.
Calculation
  • Calculation distance = speed × time, then halve it to find the distance to the surface.

Part 3 of 6Useful echoes

UseHow it works
BatsThey make a sound and work out where an insect is from the time and direction of the echo
Boats (sonar)A sound is sent down, reflects off the bottom, and the time for the echo gives the depth or the position of fish
Ultrasound scansSounds sent into the mother’s body echo back to make an image of the unborn baby
DolphinsEcho location finds food

Part 4 of 6Unwanted echoes

Recording studios
  • Recording studios echoes repeat a note and spoil the recording, so the walls are shaped or covered to stop them.
Theatres
  • Theatres designed with no large flat surfaces so voices stay clear.
Rooms
  • Rooms soft thick curtains on the walls stop echoes, while large flat mirrors or shiny metal would increase them.

Part 5 of 6Investigating reflection

1
Place a phone making a quiet sound inside or next to one cardboard tube aimed at a reflecting surface.
2
Mark the position of the tube on a sheet of paper.
3
Set the second tube near the surface and turn it until the sound is loudest.
4
Mark the second tube’s position.
5
Repeat with the first tube in a different position and with another reflecting surface.
Pattern
  • Pattern the tubes are placed at matching angles to the surface.
Surface comparison
  • Surface comparison soft foam gives a quieter reflection than a hard tile.

Part 6 of 6Modelling echo location

Model
  • Model a flashlight and mirror hidden under card model echo location.
Strength
  • Strength light reflects off the mirror like sound reflects off an insect.
Limitation
  • Limitation light is not sound and travels much faster.

Key terms

TermMeaning
ReflectionA wave bouncing back from a surface.
EchoThe reflection of a sound wave.
SonarUsing echoes of sound to find depth or objects under water.
UltrasoundSound too high for humans to hear, used for body scans.
Echo locationFinding objects using reflected sound, as bats do.
AbsorbTo take in sound rather than reflect it.

Avoid these mistakes

1
An echo is a new sound — it is the original sound reflected.
2
Soft surfaces give the best echoes — hard, smooth, flat surfaces do.
3
The distance to the wall is speed × time — the sound travels there and back, so halve it.
4
Echoes are always unwanted — bats, sonar and scans use them.

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