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Thermal Energy

Physical Science

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Thermal Energy Objectives

1. Define temperature.

2. Explain how thermal energy depends on temperature.

3. Explain how thermal energy and heat are related.

4. Compare and contrast the transfer of energy by conduction, convection, and radiation.

5. Compare and contrast thermal conductors and insulators.

6. Explain how insulators are used to control the transfer of thermal energy.

7. Understand the uses of thermal energy.

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Thermal Energy - Intro

1. What does the word thermal mean?

2. What are some words that contain thermal?

3. What is heat?

4. What are some things you do to make yourself warmer or cooler?

5. Why do you think thermal energy in important?

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Thermal Energy - Demo

1. Write a paragraph describing which beaker do you think the food coloring will spread the fastest. Why?

2. Write a paragraph describing the results of the demo. Infer why the food coloring spread through the water in the two beakers at faster rates.

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Temperature and Heat – 6.1

A. temperature- related to the average kinetic energy of an objects’ atoms or molecules

~as the temperature increases, the average speed of the particles increase

~the SI unit is the kelvin, KB. thermal energy (Q)- sum of the kinetic and potential

energy of all the atoms in an object.

1. Thermal energy increases as temperature increases

2. At constant temperature, thermal energy increases if mass increases.

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Temperature and Heat

Discussion

How do temperature and heat differ?

C. Thermal energy that flows from something at a higher temperature to something at a lower temperature is called heat

~ measured in Joules

Answer

Heat is thermal energy that flows from a warm object to a cool object. Temperature is related to the kinetic energy of atoms in an object.

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Temperature and Heat- Review Questions

1. Explain how energy moves when you touch a block of ice with your hand.

2. Describe how the thermal energy of an object changes when the object’s temperature changes.

3. When heat flows between two objects, does the temperature increase of one object always equal the temperature of the other object? Explain.

4. Explain whether the following statement is true: for any two objects, the one with the higher temperature always has more thermal energy.

Write the question and the answer. Be sure to write the heading.

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Temperature and Heat-Answers1. Explain how energy moves when you touch a block of

ice with your hand.

2. Describe how the thermal energy of an object changes when the object’s temperature changes.

3. When heat flows between two objects, does the temperature increase of one object always equal the temperature of the other object? Explain.

Write the question and the answer. Be sure to write the heading.

TE transfers as particles in your hand strike particles of ice, cooling off your hand and increasing the TE of the ice.

Temp is avg KE of particles, as KE changes, TE changes (decrease thermal energy = decrease in temperature)

No. Not all thermal energy may have been transferred.

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Temperature and Heat-Answers4. Explain whether the following statement is true: for any

two objects, the one with the higher temperature always has more thermal energy.

Write the question and the answer. Be sure to write the heading.

False. TE depends on the amount of material and the PE of the particles of the objects.

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Transferring Thermal Energy

A. Conduction-transfer of thermal energy through matter by direct contact of particles.

1. Kinetic energy is transferred as particles collide

2. Solids, particularly metals, are good heat conductors.

~Faster moving particles (greater KE) transfer thermal energy as they collide with slower moving (lower KE) particles

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Transferring Thermal EnergyB. The transfer of energy by the motion of heated

particles in a fluid is called convection.

1. Convection currents transfer heat from warmer to cooler parts of a fluid.

2. Convection currents create rain forests and deserts over different regions of the earth

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Transferring Thermal Energy

C. Radiation-energy transfer by electromagnetic waves

1. Some radiation is absorbed and some is reflected when it strikes a material

2. Heat transfer by radiation is faster in a gas than in a liquid or solid

~These waves can travel through space.

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Transferring Thermal EnergyD. Most living things control the flow of heat by using

special features such as fur, blubber, or scales.

E. Insulator-material that does not let heat flow through it easily.1. Gases such as air usually make better insulators than

liquids or solids

~Since the gas molecules are so far apart, it is more difficult for heat to be transferred

~Other good insulators-wood, some plastics, fiberglass

2. A vacuum layer in a thermos is a good insulator because it contains almost no matter to allow conduction or convection to occur.

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Transferring Thermal Energy

DiscussionWhat state of matter generally makes a good heat

conductor? Heat insulator?

Answer

Heat insulator-gases.

Heat conductor-solids, especially metals

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Transferring Thermal Energy- Review Questions

1. Explain why materials that are good conductors of heat are poor insulators.

2. Explain why the air temperature near the ceiling of a room tends to be warmer than near the floor.

3. Predict whether plastic foam, which contains pockets of air, would be a good conductor or a good insulator.

4. Describe how a convection current works.

5. Describe all the types of thermal energy transfer you might experience when you go to the beach on a hot summer day.

Write the question and the answer. Be sure to write the heading.

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Transferring Thermal Energy- Review Answers

1. Explain why materials that are good conductors of heat are poor insulators.

2. Explain why the air temperature near the ceiling of a room tends to be warmer than near the floor.

Write the question and the answer. Be sure to write the heading.

Heat passes easily through good conductors. They increase the rate at which heat is transferred. A good insulator decreases the rate at which heat is transferred.

Warm air rises because the faster moving particles are farther apart making the air dense than the cool air.

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Transferring Thermal Energy- Review Answers

3. Predict whether plastic foam, which contains pockets of air, would be a good conductor or a good insulator.

4. Describe how a convection current works.

Write the question and the answer. Be sure to write the heading.

It would be a good insulator because the air pockets do not easily transfer heat.

Convection occurs when more energetic particles move from one place to another. Convection currents transfer heat from warmer to cooler parts of the fluid.

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Transferring Thermal Energy- Review Answers

5. Describe all the types of thermal energy transfer you might experience when you go to the beach on a hot summer day.

Write the question and the answer. Be sure to write the heading.

Conduction from hot sand/concrete, convection while in the water, radiation from the sun

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Using Heat

A. Heating systems-warm homes and buildings.

1. forced-air system-fuel heats air, which is blown

through ducts and vents; cool air is returned to the

furnace to be reheated

2. radiator system-hot water or steam in a radiator

transfers thermal energy to the air

3. electric heating system-electrically heated coils in

ceilings or floors heats air by conduction

B. Solar energy -energy from the sun

1. passive solar heating does not use mechanical devices

to move heat

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2. Active solar heating systems use solar collectors to

absorb radiant energy, which is circulated through the

building.

C. Heat engine-an engine that converts thermal energy into mechanical energy

1. An internal combustion engine burns fuel inside

the engine in chambers or cylinders.

2. Internal combustion engines convert only about 26%

of the fuel’s chemical energy into mechanical energy.

D. Heat mover-device that removes thermal energy from one location and transfers it to another location at a different temperature.

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1. A refrigerator contains a coolant that absorbs heat

from the inside of the refrigerator and releases it on

the outside as heat.

2. Air conditioners cool warm air.

3. Heat pumps can both cool and warm air.

4. The human body stays cool by evaporation and

sweat.

Discussion

What are the three types of heating systems?

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Using Heat Review Questions

1. How does the thermal energy of a closed system change with time?

2. Compare and contrast an active solar heating system with a radiator system.

3. How does an internal combustion engine work?

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Using Heat Review Questions-Answers

1. How does the thermal energy of a closed system change with time?

-no heat flows across the boundary so the thermal energy stays constant

2. Compare and contrast an active solar heating system with a radiator system.

-both use hot water and radiators; in a radiator, fuel is used to heat the water and in a solar heating system, the sun’s rays (radiant energy) are used to heat the water

3. How does an internal combustion engine work? -takes fuel into the combustion chamber and burns it to convert chemical energy to mechanical energy