Heat and Temperature:

1
Chapter 14

• Heat and Temperature
• Temperature
• Energy Transfer
• Using Heat

2
TN Standards

• CLE 3202.2.3 Examine the applications and
  effects of heat energy
• CLE.3202.2.6 Investigate the Law of
  Conservation of Energy
• CLE.3202.TE.3 Explain the relationship between
  the properties of a material and the use of the
  material in the application of a technology

3
Section 1 - Temperature

• Key Questions
• 1 What does temperature have to do with energy?
• 2 What three temperature scales are commonly
  used?
• 3 What makes things feel hot or cold?

4
Temperature and Energy

• Kinetic theory of matter
• Matter is made of small particles always moving
• Higher temperature, more motion
• Large particles move slower
• The temperature of a substance is proportional to
  the average kinetic energy of the substances
  particles
• All particles have kinetic energy ( atomic )

5
Measuring Temperature

• As materials are heated, they expand
• Thermometers rely on expansion of liquids
• Mercury or Alcohol
• Thermostats rely on expansion of metals

6
Temperature Scales

• Units Fahrenheit ( English ) and Celsius (
  metric )
• Fahrenheit is English
• Celsius/Kelvin is metric
• Kelvin is an absolute scale
• Absolute zero at -273.15 oC

7
Temperature Scales - Converting

• Celsius ? Fahrenheit
• TF 1.8TC 32.0
• Fahrenheit ? Celsius
• TC ( TF 32.0 ) / 1.8

8
Temperature Scales - Converting

• Celsius ? Kelvin
• TK TC 273.15
• Kelvin ? Celsius
• TC TK - 273.15

9
Temperature Energy Transfer

• When you feel hot or cold you are detecting a
  temperature difference
• You are also feeling the affects of energy
  transfer
• Temperature changes indicate an energy transfer
  temperature difference between two objects is
  felt as heat
• Heat is the energy transferred between objects of
  different temperature

10
Section 2 Heat Transfer

• Key Questions
• 1 How does energy transfer happen?
• 2 What do conductors and insulators do?
• 3 What makes something a good conductor of heat?

11
Energy Transfer ( Heat Flow )

• What is happening in each picture
• Explain how heat is flowing ( ID how heat goes
  from one object to another )
• What might be happening on the
• atomic level?

12
Different Methods of Transfer
13
Different Methods of Transfer

• Conduction occurs between objects in direct
  contact
• Thermal Conductionheat source is one object

14
Different Methods of Transfer

• Convection results from the movement of warm
  fluids ( in contact with heat source )
• Warm fluids rise
• Cool when away from heat
• Cool fluids fall
• Convection current
• Path of warm/cool fluids

15
Different Methods of Transfer

• Radiation does not require physical contact
  between objects
• Energy transferred as
• electromagnetic waves

16
Conductors Insulators

• A conductor is a material through which energy
  can be easily transferred as heat
• An insulator is a material that transfers energy
  poorly
• Heat energy is transferred through particle
  collisions

17
Conductors Insulators

• Heat energy is transferred through particle
  collisions
• Gases poor conductors
• Why?
• Denser materials usually are better conductors
  than less dense
• Metals very good conductors
• Plastics poor conductors

18
Specific Heat

• Determines how easily energy can be transferred
  as heat
• How much energy is needed to change the
  temperature of a substance by a certain amount

19
Specific Heat

• Amount of energy needed to raise the temperature
  of 1 kg of substance by 1 K
• Energy specific heat x mass x temp change
• Energy cm?T

20
Specific Heat

• Temperature does not change when phases do
  energy goes into phase change - not temperature
  adjustment
• Latent heat Heat of Fusion
• Gives amount of energy needed for phase change

21
Heat Flow Conceptual Practice

• Scenarios Explain what is happening
• 1 You pick up a coffee cup and it is hot
• 2 You touch a glass of cold SCHAWEET tea
• 3 A breeze makes you shiver

22
Heat Flow Conceptual Practice

• Which substance can you heat the quickest?
• One with a large or small heat capacity?

23
Heat Flow Math Practice

• How much energy must be transferred as heat to
  200 kg of water ( c 4,186 J/kg/K ) in a bathtub
  to raise its temperature from 25 oC to 37 oC?

24
Section 3 Using Heat

• Key Questions
• 1 What happens to heat energy when it is
  transferred?
• 2 What do heat engines do?

25
Thermodynamics

• 1st Law total energy used in any process is
  conserved, whether that energy is transferred as
  work, heat, or both.

26
Thermodynamics

• 2nd Law energy transferred as heat ALWAYS moves
  from higher to lower temperature.

27
Thermodynamics

• Entropy randomness or disorder of a system
• Thermo tells us that total entropy of the
  universe is ALWAYS increasing ( natural tendency
  )

28
Heat Engines

• Heat Engines chemical energy is converted into
  mechanical energy by combustion

29
Heat Engines
30
Using Heat

• Rubbing alcohol applied to the skin what
  happens/what do you observe?
• Why?

31
Using Heat

• Rubbing alcohol applied to the skin what
  happens/what do you observe?
• Why?

32
Using Heat

• cooling/heating processes utilize this
• SWEATING!
• Fluidsliquids gasesare chosen that easily
  evaporate and condense
• Evaporation energy is absorbed by the
  fluid/sweat ( from surrounding air )
• Condensation energy is released by the
  fluid/moisture ( absorbed by air )