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💡 Sound moves things
Hold grains on a stretched sheet and shout near it — the grains jump, without anything touching them. Sound is carrying energy.
Activity 10.6 — Let us experiment
In this Activity, we will experiment to see that sound carries energy by making grains jump on a stretched sheet.
Activity 10.6 - Sound Carries Energy
Step 1
Stretch a sheet over a container
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Step 2
Sprinkle grains on it
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Step 3
Make a loud sound nearby
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The grains jump - sound transfers energy
- Stretch a rubber/cellophane sheet tightly over a wide container (Fig. 10.14).
- Sprinkle grains (rice, salt or chalk powder) evenly over the sheet.
- Make a loud sound near the container without touching it.
- Repeat with louder and softer sounds and different grains.
What we observe
The grains
jump
. Sound reaches the sheet through the air, makes it vibrate, and the vibration moves the grains — sound carries energy.
How does sound carry energy?
- A vibrating source transfers energy to the surrounding medium.
- Particles of the medium vibrate and collide , passing the energy along.
- This energy reaches the listener (or makes the grains jump).
ⓘ Note
- In sound propagation it is the energy that is transferred.
- The particles of the medium are not carried along.
🌎 Bridging Science and Society
- Microphones convert sound energy into electrical energy.
- Sound waves vibrate a thin membrane called a diaphragm .
- These vibrations become an electrical signal.
- A speaker does exactly the opposite.
- An electrical signal vibrates a cone, producing sound.
- So the replayed sound closely matches the captured sound.
⏸▶ Pause and Ponder
- 5. What actually reaches your ear from a tuning fork?
- Not the air particles — they only oscillate in place.
- Not the tuning fork material itself.
- Not a continuous stream of compressed air.
- Answer: (ii) the energy carried by the sound waves.
✅ Test Yourself
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What does Activity 10.6 with the grains show?
Show Answer
That sound is a form of energy — it makes the sheet and grains move. -
What travels from the source to your ear?
Show Answer
The energy carried by the sound wave, not the particles. -
Why do the grains jump higher for a louder sound?
Show Answer
A larger amplitude carries more energy to the sheet.
Important Definitions
- Energy of sound — the energy carried by a sound wave through the medium, without the particles flowing along.
