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š” 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?
- 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 .
In this Activity, we will investigate whether sound can travel through a solid.
- 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.
In this Activity, we will investigate whether sound can travel through a 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.
