Re: Why does a seatbelt buckle get hot?

Reply:

>
>If light colored objects reflect light energy, why do
>seatbelt buckles, which are light colored get so hot?
>

Hmmmm.....good question! Seat buckles are like mirrors, so they ought to just reflect the light back! There are a couple things going on here that make this work in a way that isn't what we expect. First of all, the seat buckles aren't very good mirrors. You can see your face in some of them, but they still may reflect only, oh, say 75% or so of the light that hits them.

That still doesn't explain why they feel so hot, though! The upholstery reflects a lot less than 75% of the light that hits it, but it doesn't burn you. What's going on there has to do with how well the metal transmits heat and how much it heats up with a given amount of time in the sun. The resistance of a thing to heating up when you shine light on it, pound on it, or otherwise add energy to it is its specific heat. Metals have low specific heat (compared to the upholstery), which means they heat up real fast for the same amount of time in the sun. The other reason is the conductivity of the metal that the seatbelt buckle is made of. Metals conduct electricity very well, which you know, and that means they also conduct heat very well. So when you accidentally touch it when getting into the car on a hot day, all the heat from the buckle has no trouble getting into your hand FAST!!. Ouch!

-Greg Billock

Here is a web link for a more detailed look at specific heat: http://www.physics.unc.edu/~rowan/phys24/CHAP11B.html