If you cook food at a temperature of 300 degrees it will take longer to be fully cooked than if you cooked the same food at 400 degrees. This is a simple way to explain Newton's concept of how food cooks based on the starting temperature of the food and the degree at which it is cooked. Newton's Law also explains that the external temperature of an oven effects how fast the food inside will cook; food cooks faster on days that are hot than days that are cold.
A solar oven creates a "greenhouse effect" by allowing solar energy in through the lid which comes in contact with the dark material at the bottom of the solar oven. The darker material changes the wavelength of the solar energy, and an increase in temperature results inside of the solar oven. Heat accumulates in the solar oven because more heat is remaining than is leaving the oven. This build up cooks the food within the oven.
Heat loss is explained by French physicist Joseph Fourier's Law of Heat Conduction. Fourier determined that heat will transfer from an area of high temperature to an area of low temperature. To maintain the temperature in a solar oven, it is important to thoroughly insulate the interior.
To build a solar oven you will need some newspaper, tape, scissors, black construction paper, clear plastic wrap, aluminum foil, notebook paper, a pencil and a wooden stick. Put a piece of paper on the closed lid of an empty pizza box. Center the paper on the lid and trace it. Cut the long edges on both sides of the traced paper image. Cut one of the short lines creating a fold up flap. Do not cut the remaining traced line.Wrap aluminum foil on the under side of the flap and tape the foil firmly on the outer side of the flap. Do not put tape on the inside part of the flap with aluminum foil. Put a piece of black construction paper in the bottom of the box. The black construction paper will absorb solar radiation and add to the internal heat of the oven. Place rolled up newspaper, one inch thick rolls, in the inner sides of the box for insulation and tape them in place. Finally, place one piece of plastic wrap, that has been cut one inch larger than the flap on all sides, on top of the flap and tape one side of the plastic wrap on the underside of the flap. Pull the loose wrap tight and tape down the remaining three sides of the plastic wrap. Open the flap and place another piece of plastic wrap on the inside of the flap, tape one edge on the outside and pull it tight. Tape down the remaining three sides on the outside of the flap. This will help to insulate the oven. When it is sunny, place a s'more in the center of the oven, prop open the oven with a small stick and make sure that the sunlight is reflecting inside the oven.