The big flash you see when lightning strikes is a natural electrical discharge between a cloud and the ground, or within a cloud. This lightning can travel as fast as 140,000 MPH and reach temperatures of 30,000°C. It heats the air adjacent to approximately 20,000°C - which is hotter than the surface of the sun. The temperature of the air drops quickly, causing a rapid contraction of the air. This rapid expansion and contraction of air creates intense supersonic shock wave. As this shock wave slows down to the speed of sound, you hear the thunderclap.
What causes thunder and why is a thunderclap so loud?
- Blow up a balloon so that it is near the breaking point. You are compressing the air inside the balloon.
- Set the balloon on the ground.
- Put your foot on the balloon and slowly push down. Your foot will feel a jolt as the air expands outward from the broken balloon. Although the rapid expansion of air coming from the balloon is very slight compared to the expansion caused by a lightning bolt, the principal is the same.Both cause a very loud explosive sounding noise.