04-28-2018, 07:50 AM
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.
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.