The flash of lightning due to collision of clouds is seen much before the thunder, although both occur simultaneously. This happens because the velocity of light is greater than the velocity of sound. The speed of sound depends on the properties of the medium through which it travels. The medium can vary in (1) elasticity (2) density (3) pressure and (4)temperature. The speed of sound decreases as it moves from solid to gaseous state. But in any medium the speed of sound increases with increase in temperature. The speed of sound at a particular temperature in various media are listed in the table.
| Speed of Sound in different media at 250 C | ||
|---|---|---|
| State | Substance | Speed in m/s |
| Solids | Aluminium | 5420 |
| Nickel | 6040 | |
| Steel | 5960 | |
| Iron | 5950 | |
| Brass | 4700 | |
| Glass (Flint) | 3980 | |
| Liquids | Water (Sea) | 1531 |
| Water (distilled) | 1498 | |
| Ethanol | 1207 | |
| Methanol | 1103 | |
| Gases | Hydrogen | 1284 |
| Helium | 965 | |
| Air | 346 | |
| Oxygen | 316 | |
| Sulphur dioxide | 213 | |
