Science Corner: Air pressure explained with a balloon in a bottle

Science Corner

MOBILE, Ala. (WKRG) – In today’s Science Corner experiment, learn about air pressure by learning how to blow up a balloon inside a bottle!

NECESSARY SUPPLIES: Balloon, plastic bottle, pin

STEPS (watch video for visuals):

  1. Put balloon inside the bottle, stretching the mouth of the balloon over the rim of the bottle so the balloon dangles inside the bottle
  2. Try blowing up the balloon inside the bottle. What happens?
  3. Take a pin and poke a hole in the side of the bottle.
  4. Now try blowing up the balloon. What happens now?
  5. Next blow up the balloon and while you take your mouth off of the balloon, plug hole with your finger. What do you notice?
  6. Unplug the hole and watch what happens
  7. Next put mouth over hole and suck air out of the bottle. Plug hole with finger and observe what happened.

EXPLANATION: All of this experiment is possible because of air pressure. When you blow up a balloon, the air goes from your lungs and hits the walls of the balloon – this creates air pressure that forces the balloon to inflate. When you don’t tie the balloon and let it go after being inflated, the air exits the balloon. Why? This is because you have created high air pressure inside the balloon and when you let go, the high pressure air flows out of the balloon into the low air pressure air in the room. TAKEAWAY: Air likes to flow from high to low pressure.

When you try to inflate the balloon inside the bottle without a hole, it does not work. This is because the bottle is filled with air (even though you can’t see it). With the balloon sealing the top of the bottle, the air has no where to go. As a result, there is not room for the balloon to inflate because the bottle is filled with air.

When you add a hole in the bottle, the air has an escape route. This lets the air flow out of the hole and gives the balloon room to expand.

When you inflate the balloon and then plug the hole right after, the balloon stays inflated even though the top is open. This is because of air pressure! The higher air pressure inside the balloon is pushing down on the inside walls of the balloon to keep it inflated.

When you unplug the hole, the air flowing in the hole increases the air pressure in the bottle (was previously low) and pushes up on the balloon to deflate it.

When you suck the air out of the bottle the balloon inflates without you blowing it up. When the air is sucked out of the bottle, this lowers the air pressure in the bottle. Now the air in the surrounding room is higher pressured air than the bottle. Since air flows from high to low pressure, the air in the room is forced into the ballon to fill the space created by the escaping air.

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