Heat Transfer

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Atoms and Molecules

If you have a microscope powerful enough to zoom into an object very closely, at a point, you will see molecules, then atoms. Atoms are the smallest unit of something that has its substance's properties, except it is too small to see with the naked eye. Molecules, however, are two or more types of atoms combined together. When you see ice in a drink, the molecules in it are moving very slowly, but are keeping the ice's shape. The molecules are bouncing back and forth, keeping the ice's shape easily. Any substance in a solid state has a definite shape and a definite volume. In a liquid, like water, the molecules are moving back and forth rapidly compared to the ice. The molecules are still bouncing, but they are bouncing really fast. Any substance in a liquid state has a definite volume, but no definite shape. In a gas state, the molecules are crazy. They bounce back and forth, back and forth very rapidly. Any substance in a gas state has no definite shape or volume.

So, you may wonder what this has to do with heat transfer. Atoms and molecules have a lot to do with heat transfer. Atoms and molecules have an energy called kinetic energy. Kinetic energy is the energy something has because of its motion. Kinetic energy has a lot to do with heat transfer. When one atom or molecule of a substance gets hot, it quickly bounces off the other atoms and molecules around it. The other atoms and molecules start bouncing off the atoms and molecules next to them, and so on. This process is a natural process always going on in Earth!

Convection

Have you ever seen the colored wax in a lava lamp rise up and fall down? If you have, then you have seen convection in action. The transfer of heat energy through the motions of gas, liquid, or sometimes a solid (such as sand) is called convection. But, the object that is heated up does not come in contact with the heat source. Instead, the object's molecules that are heated spread apart, and thus becomes less dense. These less dense molecules float up to the surface. The cold molecules at the surface of the object are more dense, so they flow downwards. The cold molecules at the bottom are warmed up again, eventually making a cycle that will never stop.

You can see convection almost anywhere you go! For example, when you see your mom cooking pasta, you can see some at the bottom, in midair, and the top of the popper. As you watch for sometime, you see that the kernels suddenly rise up and fall down, back to the heat source. Also, when you bake a pie in an oven, the heat from the heat source heats up the air in the oven. The heated air falls and rises. The pie in the middle of the process is baked by the air, leaving a nice and baked pie.

When you think of convection, don't get confused with conduction. Remember, in convection, the molecules touch, not the actual objects. Now, as you watch the colored blobs of a lava up rise up and fall, you can understand the real process going on.

Conduction

When you burn your finger from touching something hot, you are experiencing conduction. Conduction is another method of heat transfer. Conduction is the transfer of heat by direct contact with the atoms and molecules in solids. Heat energy always flows from a warmer to a cooler object. Unlike convection, the atoms and molecules from two substances directly touch. Plus, the atoms wiggle and shove each other but do not move freely. For example, when a spoon is kept in a steaming cup of hot chocolate, the atoms move at a constant speed. However, when the spoon rests there for some time, the part of the spoon closest to the hot chocolate starts heating up. The atoms from the hot chocolate start wiggling and pushing up. Soon, the whole spoon is hot.

Conduction is probably the most known way of heat transfer. This is because almost anything you do involves conduction! When you are in a hot shower, the hot water touches your skin. The hot molecules push and shove the other molecules. Thus, the atoms and molecules make you feel nice and warm. Also, conduction can be shown in the kitchen. If you have ever seen somebody fry something on a saucepan like a pancake, you are seeing conduction. Again, the hot molecules from the pan are transferred to the pancake batter. The batter warms up, making it into a nice and yummy pancake! Basically, the same thing happens to every two objects that are involved in conduction.

Conduction a process which can be easily confused with convection. Just remember, reader, that conduction is when two things touch, and convection is when two things don't directly touch.

Radiation

When you are outdoors cooking a pot over a fire to make a delicious meal, you are seeing radiation. Radiation is the complete process in which energy is emitted by one substance, transmitted through an intervening medium or space, and absorbed by another substance. Radiation waves travel through empty space, not anything else. The radiation waves from this fire is transmitted to the pot, which receives the waves. Soon, the pot gets hot, and transfers its heat to the food inside the pot by conduction. The food gets hot, and cooks, making the delicious meal you want to eat!

Also, when you turn on a light, you are experiencing radiation. The radiation waves from the light source travel to a point where the light waves cannot travel through the matter occupying that space.

Remember, even though there are not many examples of radiation, there is radiation in many places. Even when you stand in the sun, the radiation waves from the sun are transferred to you. You also radiate some heat to anything you touch! Reader, just remember that radiation is when waves travel through empty space, and you will be all right.


Q:How are atoms & molecules part of heat transfer?

A:Atoms & molecules are part of heat transfer because they are always moving. They move faster and farther apart when they are heated. They move slower and closer together when they are cooled.

1.While you were in your house, you notice a light bulb. What type of heat transfer did you notice?
a.Convection
b.Conduction
c.Radiation

2. At night, near your bed, you see a lava lamp. The colored blobs in it are floating up and down. What type of heat transfer is this?
a. conduction
b. convection
c. radiation

3. You are going to eat a cherry pie for dessert. When you put the uncooked pie in the oven and watch it cook, what type of heat transfer are you seeing?
a. convection
b. conduction
c. radiation

4. You find some pretty white beads in a bag. You put the beads on a bracelet, and wear it to your friend's party. While you are outside, you notice that the beads started changing color. What type of heat transfer is this?
a.Conduction
b.Radiation
c.Convection
d.b&c

5. You are in the movies waiting in line for a snack, when you notice popcorn cooking. Which type of heat transfer are you seeing?
a. Magic
b. Convection
c. Radiation
d. both b&c

6. Once you settle in the movie theater you feel warm and toasty because the heater is on. Which type of heat transfer are you feeling?
a. Convection
b. Conduction
c. Radiation
d. both a&b

7. Outside of your home, you check on your plants outside near the sidewalk. The hot sidewalk burns your feet. What type of heat transfer are you experiencing?
a. Convection
b. Radiation
c. Conduction
d. no heat transfer here

8. You toast some bread inside of your toaster. While the bread is toasting, you notice some red-hot coils in the toaster near your bread. What type of heat transfer are you seeing?
a. Radiation
b. Convection
c. Conduction

Answers:

1.c

2.b

3.a

4.b

5.c

6.a

7.a

8.a
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