Why does this work?
Solar ovens work by trapping heat energy from the Sun. In this experiment you were able to direct heat energy from the Sun through the clear plastic film using the reflective Aluminium foil flap. Once the heat was inside the pizza box, the black plastic garbage bag absorbed the heat energy and the air temperature within the pizza box rose. For best results you would have found that you need to move the box slightly to compensate for the Sun's position changes as our Earth spins. You could also further insulate the outside of the pizza box to avoid heat loss from conduction into the ground and surrounding area.
Solar ovens have been around for a long time, in fact you can buy commercial solar cookers from some boutique suppliers! The best solar cookers have means of concentrating the Sun's radiant heat energy into an area which is dark to absorb as much heat as possible and are well insulated to avoid heat loss. Solar cookers still have use in modern times, especially in areas where people don't have ready access to electricity, wood or gas cookers. There has been some revival of this technology as a response to environmental concerns of greenhouse gas emissions too, plus they make great camping gear. Of course, in cooler environments you'll have a much more difficult time!
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