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.
|
|
|
| Some older browsers have trouble playing these videos. If you are having problems, we recommend using Firefox as your browser. |
|
|
5. Crushed Can
*WARNING* This experiment uses heat and boiling water, so be sure to have an adult around to help.
This classic experiment is a fun way to learn about air pressure. We don't usually think much about the air around us, even though it plays such a vital role in our lives. it gives us oxygen to breath, carries away excess heat from out bodies, and squeezes us with over 30,000 pounds of pressure. Wait a minute! What was that last part?
For this experiment, you will need:
- several aluminum soft drink cans
- kitchen tongs or an oven mitt to pick up hot cans
- a bowl of cold water
- a hot plate or a hot skillet on the stove
You can do this experiment with only one can, but I am certain that you will want to do this one several times. Place about half an inch of water into the bottom of a soft drink can. First be sure to remove the soft drink. I suggest pouring it over some ice cream, but that is a different experiment.
If you have an electric stove, you can place the can directly on the burner. If you have a gas stove, place a skillet or pan on the burner of the stove and then place the can on the skillet. Turn the heat on low. Wait for the water in the can to start boiling.
Once the water is boiling nicely, use the tongs or the oven mitt to QUICKLY pick up the can and turn it upside down as you plunge it into the bowl of cold water. Instantly, the can will be crushed. If it did not crush well, you probably moved too slowly.
Understanding the Science
Why did the can crush? First, we have to know something about air pressure. Look up. There is a LOT of air above you, and it all has weight. We think of air as being light, but when you have a lot, it can be quite heavy. If you are at sea level, the air above you is squeezing you with a pressure of 14.7 pounds for every square inch of your body. An average human body has over 2300 square inches of skin. 2300 times 14.7 give us 33,810 pounds of pressure squeezing your body.
Then why aren't you crushed? Your body is pressurized. As the air around you pushed in, the pressure in your body pushes out to balance it. As long as the two pressures are balanced, you don't feel the pressure, but it is still there. Think about what would happen if it were possible to suddenly remove all the pressure from inside your body. Then think about what happened to the can.
When the water boils, the liquid water is changed into water vapor. This water vapor takes up a lot more space than it did when it was a liquid. A few drops of water can form enough water vapor to fill the entire can, pushing the air out through the top.
When you put the can into the cold water, the water vapor almost instantly condensed back into liquid water. This leaves very little air pressure inside the can. The surrounding air tries to rush in to equalize the pressure, but the opening of the can is under water. The water does not move into the can as quickly as the air would, and the pressure of the surrounding air crushes the can.
So now it is time to raid the recycling bin for more cans. No matter how many times I do this one, I always want to crush just one more.
Have a wonder-filled week!
