heat transfer 6(b) the student is expected to: investigate & demonstrate the movement of heat...

Heat Transfer

6(B) The student is expected to: investigate & demonstrate the movement of heat through solids, liquids, & gasses by

convection, conduction & radiation

Temperature vs. Heat

What’s the difference ?

Temperature vs. Heat

What is the difference ?

1. Temperature measures the average thermal (molecular kinetic) energy is in an object

2. Heat is the flow of thermal energy from an object of higher temperature to an object of lower temperature

Recall…

• All matter is made up of particles which are in constant motion

• “energy of motion” is kinetic energy (K.E.)

• thermal energy - the total amount of K.E. of an object

• temperature - the measured, average kinetic energy of particles in an object

Thus, the particles of higher temperature

objects move faster (have on average more K.E.)

than those of lower temperature objects

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Heat exchange occurs when faster moving

molecules (or high energy waves) transfer

energy to slower moving molecules

There are 3 methods of heat transfer…

I. Conduction II. Convection III. Radiation

I. Conduction transfer of heat by direct contact of particles of matter

Thermal conductors materials that conduct heat easily

Solids (esp. metals) conduct best because their particles are close together

Comparison of Some Thermal Conductors

Thermal insulators Materials that conduct heat poorly

Gases insulate best because their particles are widely dispersed

Air, Styrofoam & wood are good insulators; a vacuum (no air or matter) is the perfect insulator!

Thermal insulators where are they??

2. Convectiontransfer of heat by the actual motion of a fluid (liquid or gas) in the

form of currents ; warm fluids rise, cooler fluids sink

Convection Currents in Boiling Water

• The hot water rises & swirls while carrying thermal energy throughout the liquid

Convection

• Convection of air affects the weather & climates

• Large masses of air transfer heat energy by convection. Hot air is less dense so that cold air will sink while the hotter air will rise

3. Radiationtransfer of heat by electromagnetic

waves (does not need matter to travel through)

Radiation

• These waves can travel without a medium so they can carry energy through a vacuum

• Energy is released when they strike an object

Review Question 1

1. When you touch something hot, how is heat is transferred from the surface of the hot object to your hand?

Review Question 1

1. When you touch something hot, how is heat is transferred from the surface of the hot object to your hand?

By conduction, convection, or radiation?

Review Question 1

1. When you touch something hot, heat is transferred from the surface of the hot object to your hand by conduction!

This buzzard is able to soar to great heights because the air gets heated & rises. This is an example of:

A. ConductionB. RadiationC. Thermal resonanceD. Convection

Click for answer

The movement of the heated air is due to convection. Answer D.

Review Question 2

If you placed a beaker of water on the pictured hot plate, by what process would the water initially become warm?

A. Radiation from the heating surface

B. Conduction through the bottom of the beaker

C. Convection from stirring the beaker as it heats

Click on the screen for the answer.

The correct answer is B. The heat from the hot plate is conducted through the bottom of the beaker & heats the water.

Review Question 3

This is a picture of a dog showing the heat its body is producing. Is it losing heat due to:

A. Convection

B. Radiation

C. Conduction

The correct answer is B. Heat radiates from the dog’s body & yours.

Review Question 4

Review Question 5

• A cold-blooded (ectothermic) reptile lies on a rock in the middle of the day.

Which methods of heating of the lizard’s body are in play?

Review Question 5

Review Question 6

2.Metals are good conductors of heat, but gases are not. Why?

Review Question 6

2.Metals are good conductors of heat, but gases are not. Why?

Gases are poor conductors of heat because the molecules in a gas are far apart & don't bump into each other very often.

Review Question 7

3. Poor conductors of heat are good insulators. Why does a knitted hat act as an insulator?

Review Question 7

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 & air is a poor conductor.

Review Question 8

4. Give an example of how convection takes place in a liquid.

Review Question 8

4. Give an example of how convection takes place in a liquid.

warm fluids rise & cooler fluids sink creating currents which help disperse thermal energy

(much faster than would occur by conduction alone)

Review Question 9

5. How is radiation different from conduction & convection?

Review Question 9

5. How is radiation different from conduction & convection? No medium (solid, liquid or gas) is needed.

***It can pass through a vacuum!

What best explains the difference in the annual range of mean monthly temperatures between San Francisco & Wichita, Kansas?

Bonus…

Due to water’s high specific heat, large bodies of water heat & cool more slowly than land, which moderates seasonal temperature changes in marine climates

***This question deals more with properties or matter than with heat transfer!

Bonus…