posted by Clay on .
Your car has been setting out in the hot summer sun all day. The metal hood, the glass windshield, and the fabric upolstry are all at 180 degrees farenheit. If you touch the hood with your hand it could be burned, if you touch the windshield it will be very hot, if you touch the seat it will be very warm. Why is there a difference in how the different objects feel if they are all the same temperature?
The rate at which the materisl can transfer heat to your hand is proportional to k/(density*C), where k is the thermal conductivity. This parameter is called the "thermal diffusivity". The steel hood has the highest thermal diffusivity. Glass is the lowest.
The fabric absorbs most of the heat but the glass window and the metal hood cannot absorb the heat as well as the seat. This is why the fabric feels warm, but the glass window and the metal hood are very hot.