In the first part of this experiment, the bag breaks and a loud sound is heard. In the second experiment, if the people are far enough away, they should see the ball hitting the building first and the a second or two later hear the sound of the ball hitting the wall. The air rushing out of the broken bag, pushes the air outside the bag away from the bag. The air continues to move in a wave motion. A sound is head when the moving air reaches the ear.
Thunder is also the result of moving air.
As lightning strikes, energy is given off that heats the air through which it passes. This heated air quickly expands, producing energetic waves of air called thunder. In the second experiment, the ball hitting the wall causes the air to move. The ball is seen hitting the wall, first, before the observers hear the sound because light moves faster through air than sound. To reinforce this point have students measure the distant from the wall to the where they are standing.