Why does aluminum foil never get hot to the touch. You can leave it in the oven and touch it directly out of the oven without it feeling hot. Why is this?
In: Physics
[removed]
It isnt that it doesnt get hot it is that it cools off extremely quickly due to how thin it is.
EDIT : This is why a lot of heatsinks are aluminium.
EDIT #2 : Learned something. Specific heat has nothing to do with density! Seems illogical, but its true!
One key property of Aluminum is that it changes temperature really quickly.
What really happens is that it starts hot, but transfers that heat (or cools off) really quickly.
Aluminum has a very low specific heat capacity and foil is very thin, these combine together to get it a very low thermal mass (it cannot hold a lot of heat). It also has a very high surface area to volume ratio and a very high thermal conductivity. This means that the heat that it can store can move in and out of it very very fast.
When you combine these, Aluminum foil can go from red hot to room temperature in a matter of seconds. The very low thermal mass means that with very thin foil it might be 400 degrees, but putting that heat into your finger only raises your finger by 20 degrees, and results in no burn.
Not only does aluminum change temperature rapidly and lose heat to the air before you can touch it, but a sheet of aluminum foil has very little mass. This means that the total amount of stored heat in the area you touch is very low. This means that even a very hot sheet of aluminum foil can’t transfer much heat into your skin, so you don’t get burned.
Very high surface area:mass ratio.
Heat capacity is related to density (mass per unit volume), heat transfer (moving heat out of an object) is related to surface area.
The aluminum heats up to the same temperature as everything else in the oven (quite a but faster than anything else in the oven – aluminum is a good thermal conductor), but a sheet of foil has almost no mass, but tons and tons of surface area.
This means is ‘exhausts’ its heat very quickly.
If you touch foil *right* out of the oven, it is hot – but within a few seconds it has cooled down to air temperature.
[removed]
The reasons are twofold.
On the materials side, a lot of people are getting at the gist of it: a thin sheet of aluminum doesn’t have a lot of thermal energy. That’s just a property of aluminum, and also due to the fact that there’s not a lot.
The biological side is being neglected, though. You have nerve endings that measure the *movement* of thermal energy; they don’t measure raw temperature. That’s why a hot shower turns warm, and that’s where the saying about a frog in a pot comes from. Since aluminum foil doesn’t have a lot of energy to transfer, it’s hardly gonna register in your nerves.
Basically aluminium foil is so thin and conductive that all the heat doesnt get to stay in it.
Isn’t foil like only approximately 10-20 atoms thick?
Latest Answers