When we pull the plunger up, air is sucked out of the jar and the balloon seems to inflate a bit. When we push the plunger down, air goes back into the jar, and the balloon seems to shrink. The amount of air in the balloon stays the same. When we remove the air from the jar, the amount of air in the balloon is more than the amount outside the balloon, so it expands. The air is moving out of the jar.
Air is needed to allow sound vibrations to travel through the phone lines.
The valves prevent air flow. Copyright 2000 Carolina Biological Supply Company. All rights reserved.