Course 5.1Lesson 3 of 3
The speed of sound is the distance it travels in one second: about 340 m/s in air, more in liquids and most in solids. It grows a little as the air gets warmer, so we see lightning before we hear the thunder.
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Try the code and the simulations beside the lesson.
In a storm, the lightning and the thunder are made at the same moment. Yet we see the flash first and hear the thunder seconds later. Light is extremely fast; sound is much slower.
The speed of sound is the distance it travels in one second:
In air at room temperature, : about one kilometre in three seconds.
Sound travels fastest in solids, slower in liquids and slowest in gases.
| Medium | Speed of sound |
|---|---|
| Air (at ) | about |
| Water | about |
| Steel | about |
That is why you can hear a train coming by putting your ear to the rail, long before the sound arrives through the air.
In warmer air sound travels faster. A useful rule is
with in degrees Celsius: each degree adds about .
You should find that steel wins easily, water comes second, and air is last by a long way. Warming the air speeds it up only a little.
Watch out. For thunder, the sound travels one way only: . For an echo, the sound goes there and back, so you halve it. That comes in Course 5.3.
You see the flash of a firework, and its bang reaches you later. The air is at . How far away is it?
The program finds how long sound takes to cross the same distance in three media.
Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.
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