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💡 From source to ear
A sound is made over there, and somehow it arrives at your ear over here. What carries it across the gap?
What is a medium, and does sound need one?
Medium
The material - solid, liquid or gas - through which sound propagates from source to listener.
- Sound can travel (propagate) through solids, liquids and gases.
- The material through which sound travels is called a medium .
- A space with no medium (no matter) is a vacuum .
Activity 10.3 — Let us investigate
In this Activity, we will investigate whether sound can travel through a solid.
Activity 10.3 - Sound Through a Solid
Step 1
A friend knocks on a desk
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Step 2
Listen with your ear in the air
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Step 3
Press your ear to the desk and listen
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Sound is clearer through the solid desk
- Ask a friend to gently knock or scratch on a desk while you listen with your ear in the air.
- Now place your ear against the desk, close the other ear, and listen again (Fig. 10.5).
- Compare how well you hear the sound in each case.
What we observe
The sound is
clearer through the desk
— sound can travel through solids.
Activity 10.4 — Let us investigate
In this Activity, we will investigate whether sound can travel through a liquid.
Activity 10.4 - Sound Through a Liquid
Step 1
Tap two spoons in air
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Step 2
Submerge them in water
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Step 3
Tap them again under water
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You still hear it - sound travels through liquid
- Fill a tub to the brim with water and take two metal spoons.
- Tap the spoons together in air and listen (Fig. 10.6a).
- Submerge the spoons (without touching the sides) and tap them again (Fig. 10.6b).
What we observe
You still hear the tap — the sound reached you after travelling through
water
. Sound travels through liquids too.
