Please describe why a closed car heats up in the afternoon sun.?

The sun's radiant heat, heats the seats, etc. The glass allows the radiation to penetrate into the car. However, by convection, the air heats up in the car from the hot surfaces, and then the glass prevents the heat in the air from escaping. This is a mini model of the "green house" effect.

the greenhouse effect vs. "the greenhouse effect"

First of all - though I've never heard of anyone trying this - you might use the Steffan-Boltzmann law (tweeked with an average emissivity for the cars exterior) and use an approximate solar flux number...and solve for T. This should give you an average exterior temperature, which given that the car's interior and enclosed air have plenty of time to reach equilibrium, should approxmiate the interior temperature. Very well, indeed, I'd be willing to bet.

A hot car demonstrates the proper (non al gore) use of the term 'greenhouse effect' - which implies enclosing a volume to prevent mixing. "The Greenhouse Effect", so bemoaned by those who have forgotten where fossil fuels came from to begin with, is simply an increase in equilibrium temperature caused by absorbtion and reradiation of outgoing thermal IR.

The glass allows the radiation from the sun to come in but does not allow it leave that easily due to the greenhous effect. Thus radiation (light) input from the sun into the car is higher than the output which heats up the car.

It is because of the peculiar property of glass.. Glass has a particular property known as "green house effect". Heat is nothing but infra rays. The hotter the object, the lower the wavelength of the infra red rays. So the sun has infra red rays of very small wavelength. The peculiar property of glass is that it allows infra red rays of small wavelengths to pass through but does not allow infra red rays of long wavelengthts to pass through. So the sun's rays pass through the windows and heat the car and the things inside the car, but the heat generated is not lost through the windows.

A car has a high R-value (insulation) and a low E-value (Resistance to light) Just like a green house

Basicly you ca add heat quickly but it loses heat slowly.

Conduction and convection have little or nothing to do with it.

The simple answer is , In the afternoon the temperature is high and door , front and backside glasses absorb the heat and thus making the temperature inside the car very hot..

It is because the sun's heat penetrates the closed car and greenhouse effect occurs. greenhouse effect is when there is no way for the heat to go out of the car.

theory is a theory contained in the form of electro-chemical reactions which provide the philosopher the feeling of existence and truth. HAHAHAHAHAHAHA!!! only a theory............ :)