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Why does aluminum foil not get hot when it is in a hot oven?
Question Date: 2004-10-22
Answer 1:

Actually, it does get hot. In fact, if you wrap a potato in aluminum foil and put it in a hot over, the foil will get hot first. This is because metals like aluminum are very good conductors of heat, so they absorb heat very quickly. When you pull out the potato, the same property of being a good heat conductor makes sure that the foil cools down very fast.

Answer 2:

It does get hot, but since it is so thin, and an excellent thermal conductor (being metal), it radiates/conducts away all of its heat so rapidly that it cools off much faster than anything else.

Answer 3:

Actually, aluminum foil does get hot when it is in the oven. For example, if you wrap up a baked potato in foil and cook it in the oven, the foil will be too hot too touch. What you might be thinking about is, for example, laying a piece of foil in the oven (like when people make a "tent" over their turkey). If you reached into the oven, you could probably touch the foil without burning yourself. The aluminum foil has a very small mass and holds a relatively small amount of thermal energy. When you touch the foil, this thermal energy is quickly dissipated into your hand, which has much more mass. Plus, your hand is mostly made up of water, and water has a very high heat capacity (meaning it takes a lot of heat to raise the temperature of water).

If you want to think about it more quantitatively, the thermal energy being transferred goes as (heat capacity) x (mass) x (temperature change).

If you touch the foil, let's assume the case where all the energy transferred from the foil is transferred to your hand, so that:
(heat capacity of foil) x (mass of foil) x (temp change of foil)
= (heat capacity of hand) x (mass of hand) x (temp change of hand).

Now, since as we said, the heat capacity and the mass of foil are both small, this means that the foil will change temperature by a lot. On the other side, the heat capacity and mass of your hand are both large, so the temperature change of your hand will be smaller. So, while the foil is initially hot, it will cool very quickly and your hand will not "warm up" by that much.

Answer 4:

Since aluminum foil has a lot of surface area and is very thin and heat travels within aluminum very well, it is going to cool off very quickly in air when you remove it from the oven. In addition, since thin foil doesn't weigh much and thus can't hold much "heat," when you touch it not much heat can transfer to your fingers and thus it doesn't feel particularly warm. Here is a question for you:

Let's say that you are about to jump into a swimming pool. Both the air temperature and water temperature is 60 degrees F. When do you think you will feel cooler - out in the air or after you jump into the water? Why? Which do you think is better at transferring heat - air or water?

Answer 5:

Hmmmm. I don't know what kind of fancy aluminum foil you've been using, Nicole, but aluminum foil gets really hot in my oven. To understand why this happens, it's good to know what "temperature" and "heat" really mean.

Everything is made of molecules and atoms, and all atoms are made of a very heavy nucleus with a bunch of small electrons orbiting around it like moons. The temperature of an object tells you how fast the molecules in that object are moving.

When something gets really hot, its molecules get moving around really fast. When you heat up a liquid (like water), the liquid molecules start moving so fast that they stop sticking together, and they change from a liquid into a gas (this is what happens when water boils). The same thing happens when you heat up a solid (like ice) -- the molecules stop sticking together, and the solid melts into a liquid. Most of the things you use every day will melt inside an oven -- think of ice, or glass, or plastic things (please don't try to experiment with melting things in your oven!). That's because the molecules making up those things are held together pretty weakly.

But metals, like aluminum foil, are different. Instead of being made of lots of individual molecules, atoms are one big block of nuclei that all share electrons with each other. You can think of it like this: most materials (like plastic) are like a bunch of grapes -- each nucleus is weakly attached to the others by a tiny little stem. It's easy to cut the stem or knock off a few grapes if you bump into the bunch, and if you shake the bunch, all the grapes move around in different ways. But the nuclei in metal are more like the grapes in a Jell-O fruit cocktail. They're all linked together by a goop of electrons (the Jell-O), it's tough to get just one grape out without pushing a bunch of the jello around and making a big mess, and if you shake the jello, all the grapes bounce in the same way.

So when you heat up a metal, the goop of electrons (physicists call it the 'sea' of electrons) can start getting hot and moving really fast, but all the nuclei stay in the same place and just pass the electrons back and forth amongst themselves. So a metal can get really, really hot before it gets so hot that the nuclei stop sticking together. That's why you can put your aluminum foil in the oven and it will get hot, but you won't be able to turn up the heat enough to melt it.

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