Three types of heat transfer help solar cookers use the sun's energy to cook food. Heat is always transferred from the hotter object to the colder one. Additionally, heat transfers to and through some materials better than others. The three types of heat transfers are radiation, conduction, and convection. Convection is the transfer of heat by movement through materials such as air or a liquid. Materials like these are called mediums. Convection is the primary way heat can be transferred through liquids and gases. To classify a heat transfer as convection, the warm air must rise upward to equally heat the surrounding air. Box solar cookers must retain this hot air to cook the food, so the cookers must have lids with clear covers. The clear cover seals out all hot air and keeps cool air out. The second heat transfer is the transfer of heat between two objects, or substances, that are directly in contact with each other. This heat transfer, called conduction, is the primary way heat can be transferred through solids. In gases and liquids, conduction works poorly because the atoms have a lot of space between them. Because they have a lot of space between them, they cannot transmit heat to each other. Solid aluminum foil is commonly used in homemade solar ovens because it is a metal. It is well known that metal is an excellent conductor of heat. Since metal (aluminum) is an excellent conductor of heat, anything that comes into contact with it will gradually absorb the heat from the metal. The third type of heat transfer is radiation. Radiation is the transfer of energy (heat) through space using electromagnetic waves. Solar energy reaches Earth via radiation (Pearson 485). When an energy wave comes directly into contact with...... middle of paper ......p., nd Web. February 23, 2014. .•"home training tools." home training tools. Np, nd Web. 22 February 2014. .•"hyperphysics." hyperphysical. Np, nd Web. 23 February 2014. .•"solar kitchen." solar cooking. Np, nd Web. February 22, 2014. .•"solarpowerpanels.ws - Solar panel resources and information. This website is for sale!". solarpowerpanels.ws - Resources and information on solar panels. This site is for sale!. Np, nd Web. February 23, 2014. .•“teacher dominance.” teachers' domain. Np, nd Web. 22 February. 2014. .