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Chapter 6: Thermal Energy

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Insulators Reducing Heat Flow Section 3: Using Heat Heating Systems Solar Heating Thermodynamics Converting Heat to Work Heat Movers ... – PowerPoint PPT presentation

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Title: Chapter 6: Thermal Energy


1
Chapter 6 Thermal Energy
2
Section 1 Temperature and Heat
  • Temperature is related to the average kinetic
    energy of the particles in a substance.

3
Temperature Continued
  • SI unit for temp. is the Kelvin
  • K C 273 (10C 283K)
  • C K 273 (10K -263C)
  • Thermal Energy the
  • total of all the kinetic and
  • potential energy of all the
  • particles in a substance.

4
Thermal Energy Relationships
  • As temperature increases, so does thermal energy
    (because the kinetic energy of the particles
    increased).
  • Even if the temperature doesnt change, the
    thermal energy in a more massive substance is
    higher (because it is a total measure of energy).

5
Heat
  • Heat- The flow of
  • thermal energy from
  • one object to another.
  • Heat always flows from
  • warmer to cooler objects.

6
Specific Heat
  • Some things heat up or cool down faster than
    others.

7
Specific Heat Continued
  • Specific heat is the amount of heat required to
    raise the temperature of 1 kg of a material by
    one degree (C or K).
  • C water 4184 J / kg C
  • C sand 664 J / kg C

8
Why Does Water Have a High Specific Heat???
water metal
Water molecules form strong bonds with each
other therefore it takes more heat energy to
break them. Metals have weak bonds and do not
need as much energy to break them.
9
Calculating Changes In Thermal Energy
  • Q m x ?T x C
  • Q change in thermal energy (J)
  • m mass of substance (kg)
  • ?T change in temperature (C)
  • (Tf Ti)
  • C specific heat of substance (J/kgC)

10
Lets Do an Example
  • The air in a living room has a mass of 60.0kg and
    a specific heat of 1,020.0J/(kg x C). What is
    the change in thermal energy of the air when it
    warms from 20C to 25C?

11
Calorimeter
  • A calorimeter is used to help measure the
    specific heat of a substance.

12
Section 2 Transferring Thermal Energy
13
Conduction
  • Conduction is the transfer of thermal energy by
    collisions between particles in matter.
  • Conduction occurs because particles in matter are
    in constant motion.
  • Example The metal stick that the marshmallows
    are on heats up as it is near the
  • flames. The thermal energy
  • is transferred up the metal
  • stick.

14
Convection
  • Convection is the transfer of thermal energy in a
    fluid by the movement of warmer and cooler fluid
    from place to place.
  • More energetic particles
  • collide with less energetic
  • particles and transfer
  • thermal energy.

15
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16
Radiation
  • Radiation is the transfer of energy by
    electromagnetic waves. These waves can travel
    through space even when no matter is present.
  • Example Suns radiation warms Earth
  • Example When you
  • sit near a fire, radiant
  • energy warms you.

17
Radiation Continued
  • When radiation strikes a material, some of the
    energy is absorbed, some is reflected, and some
    may be transmitted through the material.

18
Controlling Heat Flow
  • Almost all living things have special features
    that help them control the flow of heat.
  • For example, the Antarctic fur seals thick coat
    helps keep it from losing heat. This helps them
    survive in a climate in which the temperature is
    often below freezing.

19
Controlling Heat Flow Continued
  • In the desert the scaly skin of the desert spiny
    lizard has just the opposite effect.
  • It reflects the Suns rays and keeps the animal
    from becoming too hot.

20
Insulators
  • A material in which heat flows slowly is an
    insulator.
  • Examples wood, some plastics, fiberglass, and
    air.
  • Materials like metals that are good conductors
    are poor insulators.

21
Reducing Heat Flow
  • A thermos bottle uses a vacuum and reflective
    surfaces to reduce the flow of heat into and out
    of the bottle. The vacuum prevents heat flow by
    conduction and convection. The reflective
    surfaces reduce the heat transfer by radiation.

22
Section 3 Using Heat
23
Heating Systems
  • Forced-Air Systems
  • Air heated in a furnace and blows through pipes
    to individual rooms to heat a home.
  • Radiator Systems
  • Closed metal container that contains water or
    steam. Thermal energy is transferred to
    surroundings by conduction, then by convection.
  • Electric Heating Systems
  • No central furnace. Electrically heated coils
    placed in floors and walls. Heat moves through
    room by convection.

24
Solar Heating
  • Passive Solar Heating
  • Radiant energy from the sun is transferred to the
    room through windows.
  • Active Solar Heating
  • Uses solar collectors to absorb solar energy
    which heats water in pipes. A pump circulates
    the water to radiators throughout the house.

25
Thermodynamics
  • Thermodynamics- the study of how heat, thermal
    energy, and work are related.
  • First Law of Thermodynamics the temperature of a
    system can be increased by adding heat to the
    system, doing work to the system, or both.
  • Example rubbing your hands together to make them
    warm
  • Second Law of Thermodynamics it is impossible
    for teat to flow from a cool object to a warm
    object unless work is done.

26
Converting Heat to Work
  • Heat engine- a device that converts heat to work.
  • It is impossible to build a device that converts
    heat completely into work!
  • Example A cars engine converts chemical energy
    in gasoline to heat, then the engine transforms
    some of the thermal energy into work by rotating
    the cars wheels.
  • Only about 25 of the heat released by burning
    gasoline is converted into work. The rest is
    transferred to the engines surroundings.

27
Heat Movers
  • A refrigerator does work on the coolant in order
    to transfer heat from inside the refrigerator to
    the warmer air outside.
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