Lesson 5 — Activity 3: Forms of Heat Transfer
Completion requirements
Lesson 5 — Activity 3: Forms of Heat Transfer
Explore
Heat flows from hot to cold. The flow continues until both objects are at the same temperature. But what really happens? How does thermal energy transfer from one object to another?
You will learn how that happens in this activity.
Conduction
What happens to the
handle of a metal saucepan when you are heating something on the stove?
The handle gets hot although it is not touching the element.
The
heat from the element is being transferred from the element to the
bottom of the pan, up the sides of the saucepan, and out to the handle.
This type of heat transfer is known as conduction.
You have learned previously that energy is transferred by the
movement of molecules or atoms in a substance. As the atoms get warmer,
they begin to move and collide with each other. As they collide, energy
is transferred between atoms. Some materials are better conductors.
Metals, for instance, are a much better conductor than plastics.
Conduction is a common method of heat transfer especially when cooking.
That is also why most handles are made of material that is a poor conductor. Never buy a saucepan with metal handles!
Convection
When you go swimming in an outdoor pool, where is the warmer water? On a hot night in July, where is the coolest and most comfortable place to sleep?
If
you guessed swimming near the surface and sleeping in the basement, you
are correct!
As liquids and gases heat and cool, they move. Warm air or liquid rises. That's why it is more comfortable to swim near the surface and not down deep. That also is why it is more comfortable to sleep in the basement on a hot night in July — the cooler air sinks downwards and settles in the basement.
This type of heat transfer in liquids and gases is called convection. Convection is used to heat and cool our homes. The heating vents in our homes are located in the floor. As warm air from the furnace blows through these vents, it warms the surrounding cooler air. As the air continues to warm, it rises to the ceiling. As it moves farther from the heating vent, it begins to cool and fall to the floor. This cycle continues, moving the warm and cool air around the room to maintain a consistent temperature. Likewise, air conditioning vents are usually located near the ceiling so the cooler air from the air conditioner cools the warmer air near the ceiling.
Did you know…
You speed up the rate of convection all the time! Each time you blow on hot food to cool it, you are speeding up the process of heat transfer.
Radiation
What do the sun and x-rays have in common? They both transfer energy through radiation.
Radiation
is the transfer of heat by electromagnetic waves. Infrared rays are
electromagnetic waves given off or radiated from the sun. When these
rays of sunlight hit an object, they make the molecules in that object
move faster. Light bulbs, toasters, and irons all radiate heat. When this
radiated heat hits the air molecules around it and the molecules begin
to speed up, the heat changes from radiated heat to convection heat
because the molecules are moving. It is this convection heat that we
feel as a result.
Radiation is commonly used in
health care practice as well. X-rays are a form of radiation that allows
a doctor or dentist to "see" inside your body.
Blausen MedicalAnnotations by Mikael Häggström, CC BY-SA 4.0
The technician places a special type of film on one side of you or your teeth and then shoots x-rays from the other side. X-rays are absorbed by your body depending on the density of the object. For instance, when you have an x-ray taken of your body, your bones absorb more of the rays than your muscles. Your bones absorb or block the x-rays from making an image on the film so therefore the doctor can "see" them. It is like the sun shining down on you, making a shadow of you. You are absorbing or blocking some of the light, so a shadow is made on the ground behind you. As a result, on the film, the doctor will "see" your bones more clearly than your muscles.
Digging Deeper
Click here to go to the Study Jams! website to watch a video that further explains what you have learned about heat, temperature, and the forms of heat transfer.
When you have finished watching the video, click on the "close" button in the upper right-hand corner to exit the video. Then, click on the "Test Yourself" button to see how much you know about the forms of heat transfer.
Self-Check
Try This!