|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
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|
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
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.
(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.
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
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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