This is why when a balloon is released, the high-pressure air flows out of the balloon to the low-pressure air surrounding it: "Winds blow from high to low. When a balloon is placed inside the bottle, it will not inflate, since the bottle is already filled with air particles with no escape route. This is a great demonstration that air takes up space.
The air inside the bottle compresses a little bit but not enough to permit the balloon to inflate. When you punch a hole in a bottle, the air molecules in the bottle have an exit. They are pushed out as a balloon fills the space inside, resulting in room for the balloon to inflate. If the hole in the bottle is then plugged, the balloon stays inflated even when the mouth is removed.
This is because the high pressure air in the balloon pushes outward harder than the low pressure air in the bottle. The air in the balloon pushes out against the walls, keeping it inflated. When the hole is unplugged, air flows back into the bottle. The air pressure in the bottle increases and collapses the balloon. An alternate demo using a glass bottle and a straw "air exit tunnel" can be seen here.
Explain how air pressure works. Download a PDF of this experiment. Blowing up a balloon with your kids might not seem like an exciting activity, but this project will let them have some fun while getting a science lesson on the side.
Well, at least for an hour or so. Use a balloon and a bottle to introduce your kids to thermal expansion and contraction, which is all around them. For example, the familiar ca-chunk that you feel driving on a bridge is actually the seams designed to allow the bridge to expand on hot days and shrink on cold days. Try this experiment with your kids to catch this phenomenon in a bottle! And not a screen in sight. When you stretch the balloon over the opening of the bottle, all of the air is trapped inside.
If they are kept in a container, such as a bottle with a balloon on top, they strike the sides of the container more forcefully. The molecules in the air are always creating pressure. Countless molecules collide into everything every second, creating a constant force.
Before the air in the balloon is heated, the molecules inside are creating as much pressure as the molecules outside, meaning that the balloon stays at equilibrium and neither expands nor contracts. When they get heated, however, the inside molecules start moving with more force. They create more pressure, causing the balloon to expand outward until the pressure equalizes. Isaiah David is a freelance writer and musician living in Portland, Ore.
He has over five years experience as a professional writer and has been published on various online outlets. He holds a degree in creative writing from the University of Michigan.
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