Why does thunder Follow lightning ?

Lightning is a huge spark of electricity . thunder is the sound the air makes as it is suddenly heated up by lightning . they both happen at the same time , but as light travels faster than sound , we see the lightning first and then hear the thunder.
Thunder is caused when lightning heats up the molecules of air along its path. The heated molecules expand , collide with cooler molecules and set up sound waves . Light travels very quickly, at about 300,000 kilometers per second. Sound is slower , traveling at about 20 kilometers per minute .