Sound waves can travel faster through solids than through air — more than 17 times faster, in some cases. In a solid, sound waves are able to be more tightly compacted than in air because there is less space between the molecules. Sound waves can travel through steel at 3.7 miles (5.96 km) per second. After solids, sound waves can travel the next-fastest through liquids. For example, sound waves travel through seawater at a speed of about 0.93 miles (1.5 km) per second. Sound travels the slowest through air, about 0.21 miles (0.33 km) in a second.
More about sound:
For every increase in seawater temperature of 7.2° Fahrenheit or 4° Celsius, sound waves are able to travel 13 feet (4 m) faster per second.
The first airplane flight to break the sound barrier — meaning to travel faster than sound — was in 1947 by test pilot Chuck Yeager.
Lightning and thunder are produced at the same time, but light travels about 1 million times faster than sound, so the thunder isn’t heard until after the lightning appears.