Why does thunder sometimes sound like a sharp 'clap' and other times like a long, low rumble?
Keep in mind that thunder is a compression, or shock wave...caused when lightning heats the air. A 'clap' comes from a single, straight lightning segment-often overhead. Rumbles, on the other hand, come from multiple bolts or branches of lightning that produce shock waves that arrive at different times. Keep in mind these shock waves are produced when the intense heat of lightning superheats air, causing it to expand faster than the speed of sound. Thunder is essentially a sonic 'boom'.