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SEA BREEZE
Air seems like the lightest thing in the world, but it actually pushes down on you and the ground with a great deal of force. This force is called air pressure. Air pressure doesn't always stay the same; meteorologists measure its changes with a barometer. When air heats up it begins to rise. When it rises, it doesn't push on the ground with as much pressure. An area full of light, warm air is called a low-pressure zone. Areas with cool, denser air are called high-pressure zones. What happens when a low-pressure zone and a high-pressure zone are right next to each other? Do this experiment to find out! Have an adult help you with the oven and matches.
Materials:
* Two metal pans
* Ice
* Sand
* Candle
* Cardboard box (if necessary)
- Set up the experiment in an area where it will be protected from drafts. If you need to, you can make a three-sided screen by cutting off one side of a cardboard box.
- Pour some sand into one of the pans and put it in the oven to heat it up. (300 degrees for 5-8 minutes.)
- While the sand is heating up, light a candle and then blow it out. Which direction does the smoke flow? If you have protected your area from drafts, it should flow straight up just like your convection current.
- Fill the second pan full of ice. Put the pan of hot sand and the pan of ice side by side. (Set the hot pan on a pot holder!)
- Light the candle again and blow it out, then hold it in between the two pans, right above the edge of the ice pan. Which direction does the smoke flow?
What happened? When you lit the candle the first time you did it in an area where the air pressure was constant, so the smoke flowed straight up. When you set the pans side by side, the ice cooled the air around it, creating a mini high-pressure zone, and the sand warmed the air around it to create a mini low-pressure zone. Air always flows from a high-pressure zone to a low-pressure zone to even up the pressure - this is what causes wind. You made a tiny breeze between the pan of ice and the pan of sand, and the smoke floated sideways in the breeze. The same thing happens between cold ocean water and hot beach sand, which is why there is almost always a breeze at the beach!
Air pressure changes cause wind, but they are responsible for other types of weather too. A low-pressure zone usually causes clouds and rain, because as the hot air rises it carries with it evaporated moisture that can condense into clouds. A high-pressure zone usually results in clear skies and sunny days because sinking currents prevent moisture from rising up and forming clouds.
Try tracking the air pressure for a few days in your area and see how it relates to the weather. You can use a barometer, or check the National Weather Service website.
