The Digital Bits Science Labs are fun science experiments for young children. Kids, make sure you have an adult's permission before trying any of these science experiments.
Digital Bits Science Lab
Science Experiments for Kids, Parents and Teachers
Learn about air pressure from a leaky bottle
Description:
A leaky bottle can teach how air pressure works, and how strong air pressure is – It can stop water from flowing!
Equipment needed:
One clear, plastic bottle with an airtight top (a two-liter pop bottle with a screw-on cap works great)
A large bowl (something big enough to hold all the water that may be in the plastic bottle)
The Digital Bits Science Lab Experiment:
Punch very small holes (less than a quarter-inch diameter) in the bottom of the plastic bottle. Three holes works well.
Fill the bottle with water. The holes will start draining the water, so you may have to turn the water on full blast to fill, or use one hand to cover the holes.
When the bottle is full, screw the top on tight. If you lift the bottle up, there may be a few drips, but after a few seconds no water should flow out. (If water still glugs out of the bottle at this point, you’ve made the holes too big.)
Unscrew the cap.
The water will start pouring out the holes in the bottom.
If you screw the cap back on before the water drains, the water flow will stop.
What’s happening here? Many things, but one big one is air pressure. With the cap screwed on, the water stays in the bottle. This is because the water needs more air to take the space at the top of the bottle, to replace the space previously filled by the water. Gravity is pulling on the water, and the water tries to flow out, but needs the air to expand and take up more space to do so. The air pressure isn’t changed – the air won’t expand or contract from the very small pull of the water. The air pressure is stronger than the pull of gravity. So the water stays in place.
If the cap is screwed on, there is nothing to replace any space used by the water. So the water doesn’t move. Unscrewing the cap allows air to flow into the bottle, which allows the water to pour out from the bottom, and the air takes up more and more space at the top.
Other articles related to this topic:
- How to join and separate two streams of water – surface tension in action
- Hot air takes up more space than cold air
- Pick up thousands of rice grains with a pencil
- Build a balloon-powered mini-hovercraft
- Learn about air pressure with a piece of paper
The text on this page states, “The air pressure is stronger than the pull of gravity. So the water stays in place.” This isn’t quite right. If the air pressure was stronger (assuming you mean it’s stronger in the opposite direction), then the water would start moving up the bottle. A more accurate statement would be, “The air pressure produces a force that is exactly as strong as the force of gravity, allowing the water to remain in equilibrium.”
hey so why cant the hole be bigger? what is the factor that makes this so? is air able to get through if the hole is too big?
” The air pressure isn’t changed – the air won’t expand or contract from the very small pull of the water.”
This is incorrect, the air pressure inside decreases to a point where the outside air pressure pressing inwards equals the force of gravity pulling the water out. It is explained well in detail here.
http://www.newton.dep.anl.gov/askasci/phy00/phy00601.htm
thank you for your help.
because of you, we can do our physics assignment.
good luck!