|Physical Science||Transformation of Energy 6C5.00||Unifying Concepts of Science||Interactions 2.4 ab|
CONTENT STANDARD: Physical Science
CONTENT TOPIC: Transformation of Energy
CONCEPT: Heat is present in all matter.
CONTENT OBJECTIVE: 6C5.00 To understand how heat is transferred
INSTRUCTIONAL OBJECTIVE: The learner will:
TN COMPONENT OF SCIENCE: Unifying Concepts of Science
BENCHMARK: Atoms and molecules are perpetually in motion.
2.4b Interactions of matter and energy shape our world.
BENCHMARK: Heat can be transferred either through materials by the collisions of atoms or across space by radiation.
Conduction is the movement of heat through a substance by the collision of molecules. Two objects must be touching for this transfer to occur. On the boundary of a hot object the faster-moving molecules collide with the slower-moving molecules on the boundary of the cooler object. In this way, the slower-moving molecules gain energy and move faster. They strike other molecule inside the cooler object. Heat energy is spread throughout the object. Conduction is a good way to spread heat energy in solids.
In liquids and gases, convection is usually more efficient. Convection is the spreading of heat energy by movements of heated liquids or gases, such as water and air. To understand how this works, picture a fireplace. As the fire heats the air around it, the warm air expands and takes up more space. The warm air is less dense and floats above the more dense cool air. The warm air rises up the chimney, taking the smoke and ashes with it. Cool air from the room flows into the fire from all sides to take the place of the rising warm air. A continuous circulation pattern of hot and cold air is set up in the room. This example of convection demonstrates how heat energy is moved around by the circulation of air.
For heat to flow by conduction or convection, matter must be present to carry the heat. In radiation, energy is transformed through matter and through empty space. Radiant energy is the transfer of heat energy by waves. It can be transferred from one object to another without contact between the two objects. The earth and the sun never touch, but the sun's energy warms the earth. Not only does the sun have radiant energy, but so does a fire, a stove, or you. A room can be heated by radiant energy from people.
To demonstrate convection, we will heat water in a clear Pyrex glass pot. As the water heats we will drop in some tiny bit of heavy colored construction paper. The bits of paper nearest the heat will move upward. Remember, hot air rises and cool air sinks. From this demonstration, give me a definition for convection. (response) (Write student definition on the board.) (Convection is the transfer of heat energy through the movement of gases or liquids.)
We will use a radiometer to demonstrate radiation. Radiant energy causes the movement of the radiometer. Give me a definition for radiant energy. (response) (Write student definition on the board.) (Radiation is the transfer of heat that does not require matter in transmission.)
Give me some examples of heating by conduction. (response) Give me some examples of heating by convection. (response)
(Pictures of the following examples would be good to have on hand; desert heat, sparks above a camp fire, person on sunny beach, person using mitt to hold tongs cooking hot dog over open fire.)
2. Metals are good conductors of heat, but gases are not. Why? (response) Use the idea of how heat is spread by conduction. (Most gases are poor conductors of heat because the molecules in a gas are far apart and don't bump into each other very often, and so, the heat is transferred slowly.)
3. Poor conductors of heat are good insulators. Why does a knitted hat act as an insulator? (Air is trapped between the fibers of a hat and air is a poor conductor.)
4. Give an example of how convection takes place in a liquid. (response)
5. How is radiation different from conduction and convection? (response)
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