Sound
Sound is a longitudinal wave made by vibrations. It needs a material to travel through. It moves at about 340 m/s in air, faster in liquids and solids.
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Analogy
Like a domino line passing a push along.
Example
Delay between flash and bang = 3 s.distance = speed x timedistance = 340 x 3 = 1,020 m
In practice
Thunder arrives after lightning because sound is much slower than light.
Practice
Flashcards
- Why can sound not travel in a vacuum?There are no particles to pass on the vibration.
Interview questions
- Describe two differences between sound waves and light waves.
- Sound is longitudinal and light is transverse
- Sound needs a material but light can cross a vacuum
- Light is much faster than sound
Questions people ask
Why can sound not travel through a vacuum?
Sound is made by particles bumping into each other and passing on a vibration. In a vacuum there are no particles to do this, so the vibration has nothing to pass along. This is why there is no sound in space, even though explosions seem noisy in films.
Does sound travel faster in solids than in air?
Yes. Particles in solids are packed tightly, so a vibration is passed from one to the next very quickly. Sound travels at about 340 m/s in air, about 1,500 m/s in water and more than 5,000 m/s in steel. That is why you can hear a train through the rail.