How does lightning cause thunder?
(Lansing State Journal, July 6, 1994)
Lightning is a massive discharge of electricity. Electricity is made up of electrons. When lightning strikes, massive amounts of electrons shoot through the air at once. In the process, they bump into a lot of air molecules. When lightning strikes, intense heat expands the air in and around it so rapidly that it results in a loud noise we know as thunder. The rumbling you hear results from the sound waves bouncing off the ground, everything on the ground, and in the clouds.
Sound travels a mile in about five seconds. To estimate how far away lightning is, count slowly when you see the flash. When you hear the thunder, divide the number your count up to by five. That will tell you how many miles away the lightning was.