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1101-C: Conduction, Convection, and Radiation 1

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1101-C: Conduction, Convection, and Radiation 1

BACK to Ladder Kinetic Theory of Matter Conceptual

This whole unit, and all of thermodynamics, is about how heat energy moves from one thing to another. There are three methods by which heat energy moves: conduction, convection, and radiation. This unit deals primarily with conduction, (the unit on fluid motion deals with convection), and the unit of electromagnetic waves deals with radiation. But, first and foremost, we need to know the difference between the three different types of heat transfer.

Vocabulary

In physics, the word fluid means a liquid or a gas.

(This is slightly different than normal English, wherein "fluids" usually refers only to potable liquids.) Liquids and gasses are fluids because the atoms and molecules can move around each other in change position; in a solid the atoms are molecules are locked into a crystal structure.

A vacuum, a space with no molecules. Nothing.

The most important example of a vacuum is outer space. Most of the universe is vacuum!

  1. What is the physics word for "nothing"?
  2. What is the physics word for the states of matter except a solid? (Those where molecules are able to change position.)
Heat transfer through touching. Molecules on the surfaces collide and exchange kinetic energy.
  • When you touch something and it is cold.
  • When you touch something and it is hot!
Heat transfer through fluid motion. Hot fluids rise, cold fluids fall.
  • Above a heater it is warm because warm air rises.
  • Below a heater it is often cold
Heat transfer through an electromagnetic wave. The only way that heat moves through a vacuum.
  • The sun sends heat to the earth through electromagnetic waves (radiation).
  • Fire and other very warm things that light up bright red.
  1. Which is the only way that heat can travel through a vacuum?
  2. Which type of heat transfer involves fluid motion?
  3. Which type of heat transfer involves things touching?
Heat Conduction

Touching ice: heat leaves your hands.

Heat goes into the chicken.
Heat Convection

Warm air is rising, and cold air is falling.

Water is also a fluid, so water can have convection also.
Heat Radiation

The sun sends heat to the earth through electromagnetic waves.

A heat lamp shines electromagnetic waves on food.

For each picture, write if it shows conduction, convection, or radiation.

For each statement, write if it represents an example of conduction, convection, or radiation.

  1. Warm air coming out of the top of the heater.
  2. Chicken touches a frying pan.
  3. Heat from a microwave oven.
  4. Heat that travels from the sun to the earth.
  5. Drink a cold cup of water, and heat leaves your tongue.
  6. Warm water rises to the top of a pot of boiling water.
Your Own Examples:
  1. Give 2 real life examples of CONDUCTION:
  2. Give 2 real life examples of CONVECTION:
  3. Give 2 real life examples of RADIATION:

Fire!

Fire can actually include all three different types of heat transfer.

While fire can employ all three methods of heat transfer, it is certainly most closely associated with radiation. The main reason that people light a campfire, so that it heats them and lights them with electromagnetic waves. They don't touch the fire or stay on top of a fire.



If you actually touch a fire, that is is heat conduction.


The air above a fire is warm because of heat convection.


But the main way we are heated by fire is that it radiates heat in all direction. You can tell it is radiating heat because it is giving off so much LIGHT (electromagnetic waves!)
A summary:

For each statement, write if it represents an example of conduction, convection, or radiation.

  1. You touch a fire.
  2. Hot air rises out the top of a fire.
  3. Heat emanating out of the fire in all directions.

Applications

  1. Imagine you are going to a football agem in December. It is very, very cold. You need to sit on a metal bleacher.
    1. How will the metal bleacher feel?
    2. Why is it cold?
      1. conduction
      2. convection
      3. radiation
    3. Which of these is happening?
      1. heat is leaving your body
      2. cold is entering your body
    4. If you are smart, you brought a cushion!

      How does the cushion keep you warmer?

  2. In a fire, you are told to "Stop-Drop-and Roll" Why do you need to drop? Why is it important to be close to the ground?
  3. There are seven types of electromagnetic wave: radio, micro, infrared, visible light, ultraviolet, X-ray, and gamma ray. All of these can cause heat radiation, but the one most typically responsible for heat radiation is infrared waves.
    The word "radiation" can seem very scary, but in physics, "radiation" refers only to the electromagnetic waves. (For a longer treatment of this issue, see this pod).
    Write two things that are definitely not dangerous but are still considered radiation.
  4. Things that are radiating heat are often bright red!

    Which of the seven types of electromagentic wave is it giving off?
  5. How can you tell that a fire is radiating heat?

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