Building your own solar oven with The Physics Experience
Next time you order out for pizza, don't throw away the box! Build your own solar oven instead!
This activity will teach you how to manage all three methods of heat transfer (how heat energy moves from one place to another).
CAUTION: THIS OVEN CAN REACH TEMPERATURES UP TO 200 DEGREES F. ALWAYS HAVE AN ADULT HELP YOU WITH THIS.
All ordinary stuff (a.k.a. matter) is made of atoms. ALL atoms are ALWAYS moving. Heat energy is simply how fast the atoms (and little clumps of atoms called molecules) are moving. (Faster atoms = hotter stuff!)
The heat energy we get from the sun really isn't heat energy - it's LIGHT! ALL moving atoms give off light energy. The faster the atoms move, the more light they give off. Light energy can be absorbed by stuff and turned back into heat energy. This heat transfer process - going from heat to light and back to heat - is called radiation.
Dark things, like black paper, are especially good at turning sunlight into heat. That's why we line the pizza box with it! And, shiny things like aluminum foil mostly bounce the light off, instead of absorbing it. Lining the lid with foil reflects more light into the oven - which makes the oven hotter!
Moving atoms can bump into nearby atoms, making THEM move too. This heat transfer process - where heat energy is going from atom to atom - is called conduction. Conduction generally works best in metals and other conductors. But we want the heat to stay inside our oven! So we make the oven out of cardboard (the pizza box), and line it with newspaper. Cardboard and paper are called insulators, because they don't conduct heat well.
Air atoms and molecules are special. When they move fast, they go all over the place! Which means they spread out. When air spreads out, it's LIGHTER than the cooler air nearby. So it rises. Cooler air moves in, heats up, and rises. Heat transfer by moving around hot stuff (like air, water, etc.) is called convection. A layer of clear plastic wrap on top of our oven lets sunlight in, but keeps hot air from escaping.
Earlier I said that ALL warm stuff give off light. It may not look like it, but your oven gives off light too! It's a special INVISIBLE light called infrared light. The plastic wrap will help keep a little of the infrared light inside the oven. Glass is much better: it lets visible sunlight into the oven, but blocks the infrared light from escaping. This is called the greenhouse effect. It's the reason why greenhouses (and your car!) get hot in the sun. CAUTION: GLASS IS SHARP, AND BREAKS EASILY. ONLY USE GLASS WITH HELP FROM AN ADULT.
If you do a good job, your oven might reach 200 degrees F! (This is hot enough to break / melt most ordinary thermometers. Use a meat thermometer or infrared thermometer instead). CAUTION: HOT THINGS CAN BURN YOU. ALWAYS HAVE AN ADULT HELP YOU WITH THIS.
Want to learn more fun physics? Schedule me for a presentation of The Physics Experience at your school, library, scout troop, birthday party, or whatever! My contact information is on the NBC15 website.