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Dear Expert, My name is Anton I am a 4th grade student at Stratham Memorial School. I am researching about thermal, geothermal and biomass energy with a couple of friends. I've learned that a snowman has more thermal energy than a hot cup of chocolate, because the snowman is bigger. I have also learned that conductors are the best way to make heat. Metal is a good conductor. Rubber and plastic are insulators. They don’t let thermal energy pass through them easily. I learned a very interesting fact about geothermal energy, when tectonic plates separate some of the heat from the earth's core rises. I also have some questions to ask you.
1. If aluminum foil is a type of metal why doesn’t it get hot when you use it for cooking?
2. What are the three types of heat transfers?
3. How does convection current work in a pot of boiling water?
And last how do you make heat resistant clothes and what do you make them out of?
Thank you for taking your time to help me research. Please contact my teacher , or mail a response to my school (39 Gifford Farm Rd. Stratham, NH 03885). Thank you! Sincerely,
Question Date: 2019-02-27
Answer 1:

Aluminum foil does in fact get hot when it is used for cooking. When you put foil into the oven and keep it at baking temperatures for a little while, you'll notice that the foil is actually hot when it first comes out of the oven. However, because aluminum foil is a metal and therefore an excellent heat conductor, it both gains AND loses heat very quickly. Furthermore, since foil is very thin, it gains and loses heat even faster than a block of aluminum would. Because of how fast aluminum foil loses heat energy, you don't feel the heat as much any more as soon as it's out of the oven for even a few minutes, but it is still necessary to use heat-insulating gloves to pull foil out of the oven!

2. Heat can be transferred in a few ways, and they're not all completely separate, so let's talk about the broad categories. Heat can be conducted from one thing to another - say a hot pan onto a spatula - by conduction, which happens when the very very small particles that make up matter move and collide into other such small particles. The particles with more energy, when colliding with other particles, will give some of this energy to the initially lower-energy particles and thereby transferring the heat. If we go back to our hot-pan-spatula example, the particles of the hot pan that are in contact with the spatula are moving even though we can't see the movement, and the hot-pan particles actually touch the particles in the spatula such that the spatula particles get some energy and become hot. This is the mechanism known as heat conduction.

Another way heat is transferred is through radiation. Radiation is something everything is doing constantly, but hotter things radiate more heat. In this case, what makes us feel the heat are things called electromagnetic waves. We feel heat radiated from the sun or a fire because of these waves, and you'll learn much more about them later. A third type of heat transfer that we know as convection describes how heat moves in liquids and gases. This is often categorized separately because the particles in liquids and gases can move more than the particles in solids (water can flow more easily than a hot pan or a spatula).

3. Your second question leads us to the answer of your third question. The fact that water particle can move more means that when a container of water is heated, the hot particles, which first sit at the bottom of the container (assuming you're heating the water by putting it in a pan and setting it down on a stove), will now rise toward the top because the heat these particles are gaining makes them move faster and cause them to separate from each other more than the colder particles. Now there is more space between the hotter particles than between the colder particles, meaning that the colder regions in that container of water are now denser (a larger number of particles in a colder teaspoon of water than in a hotter teaspoon of water). Denser things sink, so the colder water sinks, and hotter water rises. Now the colder water will be heated by being closer to the stove (incidentally, conduction is responsible for heat transfer between the stove and pan themselves and the water). The process of water movement repeats until all the entire container of water is at boiling temperature or until someone turns off the stove.

4. How clothing is made depends on where and why the clothing is worn. For instance, oven mitts, which are heat-resistant, can simply be made by stacking very thick fabric together to slow the heat from transferring because fabrics are usually bad heat conductors; oven mitts can also be made from silicone, and silicone is made by chemical reactions that link many small molecules together into chains of these molecules (molecules are just units of chemical substances, like Lego blocks are units of Lego models). Different types of silicone are mixed and molded into the shapes we want, including oven mitts.

Flame-resistant clothing is a little different. It can be made out of cotton, but the cotton receives treatment from a special chemical that turns into carbon (black carbon) when exposed to a flame such that the fire does not spread on the surface of the clothes. For clothing that can stop molten metal, manufacturers use Kevlar threads to make the fabric, and aluminum on the outside of the clothes to reflect the heat from the metal such that the heat does not transfer onto the person inside the clothing.


Answer 2:

(1) Aluminum is a type of metal. Aluminum foil is just a very thin sheet of aluminum. Metals conduct heat well and so get hot quickly, especially when there is little mass (which there isn't, because the sheet is so thin).

(2) Heat can be transferred by conduction (heat traveling between two objects in contact with each-other) , by convection (movement of hotter and cooler material that moves heat with it), and radiation (hot objects emitting light, that carries energy with it).

(3) The bottom is hotter because it's closer to the flame, and the top is cooler because water is evaporating, which consumes heat. From our database a scientist mentions that "this is due to diffusive heat transfer. Basically, even if the water does not look like it is moving overall, the water molecules are still bumping into each other and moving around in the pot. The water molecules at the bottom of the pot, which are moving faster due to all the heat energy they have absorbed from the flame, begin to bump into water molecules above them. They transfer energy through these collisions, and eventually the heat begins to reach the top of the pot, and the water evaporates.

Heat-resistance in clothes is something different depending on what you are referring to. It could mean clothes made of material that doesn't melt, or it could be materials that trap air and, with it, heat.


Answer 3:

To answer your first question, the aluminum foil does get hot! It’s a very good conductor, and gets hot quickly even before the food you’re cooking does. When you pull your food out of the oven, that same property of heating up quickly helps it cool down quickly. That’s why it doesn’t feel so hot when you touch it after.

To answer your second question, the three types of heat transfer are conduction, convection, and radiation.

Conduction is heat transferred through solid material like how the metal handle on a pot gets hot on the stove. Convection is heat transferred though liquids and gases, like the air heating up the oven. And radiation occurs through electromagnetic radiation, like the heat output from chemical reactors.

For your third question, when you put a pot of water on the stove, the burner heats the pot, which warms up the water inside. The hot water rises to the top, and the cold water moves to the bottom, which creates a circle motion. This eventually heats all the water.

Finally, heat resistant materials include fiberglass and silicone-coated cloth. They protect against heat and if they light on fire, extinguish easier. They protect people who are around high heat environments, like firefighters.



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