Notes from Janice’s Desk
This morning I noticed that a sealed gallon-size plastic water bottle was partially crushed. Further investigation revealed that the floor around the bottle was wet. It was obvious that the water had leaked out. But if the bottle has a hole in it, why didn’t all of the water leak out?
I pondered the question for a few minutes and mentally listed facts that might help explain the phenomenon.
1.FACT: For any pliable plastic container to maintain its shape, the air pressure inside and outside the container must be equal.
For the plastic water bottle to be crushed, the pressure inside the bottle had to decrease so that the pressure outside pushed it in.
So what caused the pressure inside the bottle to decrease? UMMM!
2. FACT: Air molecules, like any gas, will spread out and fill the container they are trapped in. Thus air pressure decreases inside the closed container.
The plastic bottle was crushed by the air pressure outside the bottle.
3. FACT: The crushed bottle had less space inside. The air molecules had to get closer together. This caused the air pressure inside the bottle to increase.
When the pressure outside and inside the bottle were equal, the water stopped pouring out of the hole.
SCIENCE CHALLENGE: How does the position of the hole in the bottle affect the amount of water that leaks out?
For more information, see AIR PRESSURE: WHAT IS IT?