Blow into the brown paper lunch bag and fill it up with air.
Twist the open end and close with your hand.
Quickly hit the bag with your free hand.
Hitting the bag causes the air inside the bag to compress so quickly that the pressure breaks the bag. The air rushes out and pushes the air outside away from the bag. The air continues to move forward in a wave. When the moving air reaches your ear, you hear a sound. Thunder is produced in a similar way. As lightning strikes, energy is given off that heat the air through which it passes. This heated air quickly expands producing energetic waves of air resulting in a sound called thunder.