Sound
Sound is something vibrating and pushing the air beside it, which pushes the next bit. It does not travel alone: it needs matter, which is why no explosion would be heard in space. The closer the particles, the sooner the push passes on, so it goes at 340 m/s in air, 1,500 in water and 5,000 in steel. More vibrations per second is heard as higher, and more amplitude as louder: two different things, confused all the time.
Where this sits
- Comes after
- Waves
Exercises from this rung
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Through which does sound travel fastest?
- steel
- a vacuum
- water
- air
Why Through steel, at about 5,000 m/s: the closer the particles are, the sooner they pass the push along. In water it is 1,500 and in air 340. In a vacuum it does not travel at all, because there is nothing to vibrate: that is why no explosion would be heard in space.
easierWhich one sounds higher?
- The first one
- The second one
- They sound the same
Why The first one vibrated 2 times faster, and faster means higher. That is all “high” means: more vibrations per second. A guitar's short string vibrates more times and so it sounds higher up.
in betweenYou shout at a mountain and the echo comes back after 1 s. How far away is it?
Answer 170
Why In 1 s sound covers 340 × 1 = 340 m, but that is the round trip: the mountain is half that away, 170 m. Forgetting the path is travelled twice is the standard mistake.
harder