One of my goals with these science videos is to provide support to the homeschool community. After years of writing the Experiment of the Week, and presenting science shows for homeschool groups, I have been impressed with how strongly homeschool families are involved with hands-on science. I have also seen the need for a science curriculum that fulfills their educational needs. Starting with these videos, I hope to offer the homeschool community some of the science education support that they need, as well as a fun way to get students involved with scientific discovery.
I also try to use activities that involve common items. Most homeschoolers don't have access to test tubes, flasks, chemicals, microscopes and other scientific equipment. In the future, I hope to be able to guide them to inexpensive sources for science equipment to enrich their science curriculum.
This is a science experiment that can also be used to trick your friends. We are going to use air pressure to control the flow of water through a hole in a 2 liter bottle.
To find out, you will need:
- an empty, 2 liter soft drink bottle
- a straight pin or small nail
- a pair of pliers
- water
Fill the bottle with water and place the cap on tightly. Use the pliers to hold the pin and use it to make a small hole about half way down the side of the bottle. Holding the bottle over the sink, remove your finger from the hole. After a tiny bit of water escapes, it will stop flowing. The hole is still there, as you can see by gently squeezing the bottle, but if you leave it undisturbed, the water stays inside.
Still holding the bottle over the sink, loosen the cap of the bottle. You don't have to remove the cap, just loosen it a bit. Instantly, the water will begin to flow from the hole. Tighten the cap and the water will stop flowing. Why?
Understanding the Science
When the water initially flows from the hole, nothing goes in to take its place. The hole is too small to let air in while the water is flowing out. Water flowing out lowers the pressure inside the bottle. Then the air pressure outside then stops the flow. At that point, there is a balance between the pressure inside and the pressure outside. As long as that balance is in place, the water stays in the bottle. if you squeeze the bottle gently, you are increasing the internal pressure, and the water flows. Release the bottle and watch closely. You may see tiny bubbles of air being pulled in through the hole, restoring the balance of pressure.
When you loosen the cap, air can flow in. The balance of pressure is upset, and again the water flows. When you tighten the cap, the water will continue to flow briefly, until the balance is restored. Someone that liked to play tricks might be tempted to use this to play a trick on a friend, handing them a bottle of water that had several pin holes in it, but of course, I would never do that.
Have a wonder-filled week.
