The Law of Thermodynamics says that two bodies will eventually have equal temperatures. How is it possible that when you leave your car in the sun, it gets hotter in the car than it is outside? Why isn’t the car at the same temperature as the outside, as it should be according to the Law?
Answer
Law of Thermodynamics says that two bodies eventually will have equal temperatures.
That is not an absolute Law. There are conditions, and one of those conditions involves the energy input to the bodies. If this Law was absolute, then the Sun would be at the same temperature as the universe, about 2.7 K, because the universe is much larger than the Sun. But the Sun has an internal energy converter/source which raises its local temperature.
The interior of a closed car in the sunlight will be higher because of a greenhouse effect. The glass of the car is transparent to the visible light, so that energy is absorbed by the interior of the car (the seats, dashboard, and floor) increasing their temperature. Those items then emit infrared radiation and the glass is fairly opaque to that radiation and the energy stays in the car. So more energy comes in the glass than is escaping out of the glass.
Because the trunk/boot doesn't have a glass opening to let radiation in, it will generally stay quite a bit cooler than the passenger compartment. Whatever radiation the trunk lid gets is reflected and radiated back out fairly efficiently. That's not to say it doesn't get hot, but it doesn't get to the same as the passenger compartment.
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