1. Chapter 6 Thermal Energy
Section 1
Page

2. Temperature and Heat What do we observe about hot and cold?
Can we see hot?
We can compare hot and cold by touch.
Hot and cold are subjective
For me, 72% is cold, for my wife it is hot
Swimming
If a hot object and a cold object are placed side by side in an enclosed container, they come to the same temperature.

3. Temperature and Heat (cont)
Hotter the temperature, the more heat
Heat can flow from a hot object to a cooler object.
Early theory explained heat as a substance called caloric
Does an object weigh more when it is hot?
Caloric therefore must be weightless

4. Particles in Constant Motion

5. Modern Theory Kinetic Theory of Heat Page 476
Matter is made up of tiny particles, atoms and molecules
These particles are in constant random motion
Move in all directions until they strike something
Kinetic energy = ½ mv2
More mass of the particle, more energy, more heat
Greater speed, more energy, more heat
Potential energy
Particles attract each other so when separated they have potential energy.

6. Heat/Thermal Energy
Thermal Energy is the total kinetic and potential energy of the particles making up an object.
Heat is thermal energy that flows from an object at a higher temperature to an object at a lower temperature.
Heat always flows from higher temperature to lower temperature.

7. Temperature
The temperature of an object is a measure of the average kinetic energy of the particles in an object.
Higher temperature, more kinetic energy
Lower temperature, less kinetic energy
Temperature is measured by comparing characteristics of a substance that changes with temperature.
The volume of most substances change with temperature

8. Thermometers Celsius or centigrade Fahrenheit Kelvin 212o 100o 373o
Boiling temp of water 0o
273o
32o
Freezing temp of water
-273o 0o
Celsius or centigrade
Fahrenheit
Kelvin

9. Heat
Heat is thermal energy that flows from an object at a higher temperature to an object at a lower temperature.
Heat always flows from higher temperature to lower temperature.
Since energy is conserved, heat that flows from one object must be gained by other objects.

10. Heat Quantity
At noon on the beach, how does the temperature of the air, the water and the sand compare?
The more heat that is added to an object, the higher the temperature rise.
The amount of heat required to raise the temperature of an object depends on the material.
The amount of heat (Joules) required to raise the temperature of 1 kg of material by 1oC is called the specific heat. (Page 161)

11. Quantity of Heat Q = quantity of heat, measure in units of Joules
m= mass, measured in kilograms (kg)
Tf = final temperature, units of oC
Ti = initial temperature, units of oC
C = specific heat (c- used in most textbooks)
The quantity of heat required to raise the temperature of 1 kilogram of substance by 1oC
The units are J/kg oC
Q = m (Tf - Ti )C or Q= mc ∆T
∆T = (Tf - Ti )

12. Specific Heats (P161) Aluminum 899 Gold 129 Concrete 880 Copper 386
Substance
Specific Heat (J/kg Co)
Aluminum
899
Gold
129
Concrete
880
Copper
386
Diamond
518
Ethyl Alcohol
2400
Glass
837
Iron
447
Water
4186

13. Definitions
Temperature – (measured with a thermometer) – a measure of the average kinetic energy of the particles that make up an object.
Thermal Energy – the sum of the kinetic and potential energy of the particles in an object.
Heat – thermal energy that is transferred.
Specific heat – the amount of heat that is needed to raise the temperature of 1 kg of a substance by 1 oC
Q = m (Tf - Ti )C or Q= mc ∆T
The heat lost by one object must be gained by some other object.

14. Practice Problems p162: 1-3, P 163: 6,7
A wooden block has a mass of 20.0 kg and specific heat of 1700 J/kg oC. Find the change in thermal energy of the block as it warms from 15 oC to 25 oC.
Given
Asked?
Formula: Q = m (Tf - Ti )C or Q= mc ∆T

15. Practice Problems p162: 1-3, P 163: 6,7
The air in a living room has a mass of 60.0 kg and specific heat of 1020 J/kg oC. What is the change in thermal energy of the air when it warms from 20 oC to 25 oC.
Given
Asked?
Formula: Q = m (Tf - Ti )C or Q= mc ∆T

16. Practice Problems p162: 1-3, P 163: 6,7
The thermal energy of water in a mug increases by 12,552 J when the water is heated from 20 oC to 40 oC. If the specific heat of water is 4,184 J/kg oC, what is the mass of the water?
Given
Asked?
Formula:Q = m (Tf - Ti )C or Q= mc ∆T

17. Practice Problems p162: 1-3, P 163: 6,7
A block has a mass of 0.20 kg, a specific heat of 710 J/kg oC and is at a temperature of 20 oC. What is the block’s final temperature if its thermal energy increases by 2,130 J?
Given
Asked?
Formula: Q = m (Tf - Ti )C or Q= mc ∆T

18. Practice Problems p162: 1-3, P 163: 6,7
Calculate the change in thermal energy of the water in a pond with a mass of 1,000 kg and a specific heat of 4,184 J/kg oC if the water cools by 1 oC.
Given
Asked?
Formula: Q = m (Tf - Ti )C or Q= mc ∆T

19. Practice Problems p162: 1-3, P 163: 6,7
Calculate the specific heat of a metal if 0.5 kg of the metal absorbs 9,000 J of heat as it warms by 10 oC.
Given
Asked?
Formula: Q = m (Tf - Ti )C or Q= mc ∆T

20. Chapter 6 Section 2 Transferring Thermal Energy
Page

21. Transfer of Thermal Energy
Conduction – thermal energy is transferred by the collision of particles with high kinetic energy with particles of lower kinetic energy.
Metals are good conductors
Convection – the transfer of thermal energy in a fluid (liquid or gas) by the movement of warmer and cooler fluid from place to place
Radiation- the transfer of thermal energy by electromagnetic waves (light, infra-red, ultraviolet, microwaves)

22. Controlling Thermal Energy Transfer
Reflective surfaces reflect radiation and do not let the radiation pass.
Vacuum prevents both convection and conduction.
Air spaces prevents conduction.
Examples
Attic insulation
Thermos bottle
Clothing

23. Calorimeter (page 163)

24. Vacuum Bottle

25. Chapter 6 Section 3 Using Heat
Page

26. Definitions
Temperature – (measured with a thermometer) – a measure of the average kinetic energy of the particles that make up an object.
Thermal Energy – the sum of the kinetic and potential energy of the particles in an object.
Heat – thermal energy that is transferred.
Specific heat – the amount of heat that is needed to raise the temperature of 1 kg of a substance by 1 oC
Q = m (Tf - Ti )C or Q= mc ∆T
The heat lost by one object must be gained by some other object.

27. Transfer of Thermal Energy
Conduction – thermal energy is transferred by the collision of particles with high kinetic energy with particles of lower kinetic energy.
Metals are good conductors
Convection – the transfer of thermal energy in a fluid (liquid or gas) by the movement of warmer and cooler fluid from place to place
Radiation- the transfer of thermal energy by electromagnetic waves (light, infra-red, ultraviolet, microwaves)

28. Heating Systems Source of Heat Transfer of Heat
Burning Fuel (propane, fuel oil, coal, wood)
Electrical Resistance heating
Solar Heat – absorbing heat from sun light
Transfer of Heat
Radiant Heat – old fashioned fireplace or stove
Force Air – Fan blows air through ducts and vents p172
Circulating Hot Water or Steam – pump and radiators
Heat pumps – as a gas expands it absorbs heat as it contracts it gives off heat

29. Typical Forced Air

30. Solar Energy
Passive solar – designing buildings to absorb and store heat directly from sunlight.
Orientation
South facing windows
Materials the store heat
Active solar – systems that use sunlight to heat fluid (usually water) these fluids are then pumped to areas needing heat.

31. Passive Solar

32. Active Solar

33. Thermodynamics Thermodynamics – movement of heat
Study of the relationships between work, thermal energy and heat.
First Law of Thermodynamics
In ordinary chemical and physical reactions, energy cannot be created nor destroyed.
The increase in thermal energy of a system must equal the work done on the system and the heat transferred to the system

34. Laws of Thermodynamics
Second Law of Thermodynamics
Energy always tends to go from a more usable form to a less usable form
It is impossible for heat to flow from a cooler object to a warmer object unless work is done on the cooler object.

35. Converting Heat to Work Steam Engines
Steam engine uses fuel to heat water and turn it into steam.
The steam is then used to push the blades of a turbine.
Pushing the turbine uses up some of the energy of the steam and the steam condenses back to water.

36. Changing Heat to Work (cont) Internal combustion (p177)
Internal combustion engine
Gasoline (or other fuel) vapors are mixed with air.
Piston compresses the fuel/air mixture
Spark plug ignites the fuel/air mixture
The explosion produces hot gases (carbon dioxide and carbon monoxide) which expand
Expanded gases push the piston down again.

37. Internal Combustion Engine

38. Converting Work to Heat (p175, 177)
Pushing the bicycle pump handle compresses air.
Pushing the pump handle also generates heat.
Friction of the pump
Compressing the air
Friction from the parts of an automobile produce friction which generates heat.
Heat is usually a wasted byproduct of work
Second Law of Thermodynamics

39. Refrigerator p178 Second Law of thermodynamics (Page 175)
It is impossible for heat to flow from a cool object to a warm object unless work is done on the cool object.
A refrigerator takes heat from the cold inside of the refrigerator and transfers it into the hot room.
Impossible to move heat from a cold object to a warmer object unless we do work on the colder object.

40. Refrigerators and Heat Pumps
Special materials – freon
Freon changes to a gas at a low temperature if the pressure is high.
Freon absorbs heat as it is changed into a gas.
The heat is absorbed from the surrounding air.
A pump (compressor) then compresses the Freon and it turns back to a liquid, but in the process gives up heat.
These two processes take place at low temperatures.

41. Refrigerators and Heat Pumps

42. Heat Pump Refrigerator or Heater
Freon absorbs heat as it is changed into a gas.
Compressor
Heat Absorber
Expansion Valve
compresses the freon and it turns back to a liquid, but in the process gives up heat.
Heat Emitter

43. Human Heating and Cooling

44. Human Coolant
Evaporation of a liquid to its gaseous form (vapor) requires energy.
Evaporation of sweat on the body takes heat energy from the body and uses this to convert the sweat to water vapor.
Heat is conducted to the surface of the skin by blood vessels opening up to allow more blood flow.
In cold weather, the blood vessels close down to prevent heat loss.
We shiver to generate more heat.

45. Calorimeter (page 163)

46. Heat Transformed Energy (heat) is not created or destroyed.
Heat lost by the metal = heat gained by water and cup
Heat lost = mmetal (Tf – Ti ) cmetal
Heat gained= Qwater + Qcup
Qwater = mwater (Tf – Ti ) cwater
Qcup = mcuo (Tf – Ti ) ccup

47. Specific Heat of Metals
Steel J/g oC
Copper
Tin
Zinc
Silver
Gold

48. Chapter 6 Assignments Chapter 6 Test 11/29
Thermal Energy Equation Problems
Page 162: 1,2,3
Section Review Page 163 Applying Math #6, #7
Specific Heat Lab
NTWS Chapter 6 Sections 1-2
Worksheet with Problems-
Worksheet Chapter 6 Section 3
Chapter 6 Review-Pages /28
Questions 7,8,10, ,
Chapter 6 Test 11/29

49. Q= m(Tf –Ti ) C
23. How much thermal energy is needed to raise the temperature of 4.0kg of water from 25o C to 75 oC?
Given:
Asked:
Substitute:
Math:
Answer with units

50. Q= m(Tf –Ti ) C
24. How does the temperature of 33.0g of graphite change when it absorbs 350J of thermal energy?
Given:
Asked:
Substitute:
Math:
Answer with units

51. Q= m(Tf –Ti ) C
25. A hot iron ball is dropped into 200.0g of cooler water. The water temperature increases by 2oC and the temperature of the ball decreases by 18.6oC. What is the mass of the iron ball?
Given:
Asked:
Substitute:
Math:
Answer with units