1. Thermal Physics

2. Change of State (Phase) of Matter
There are 3 states (phases) of matter:
Solids, liquids and gases
When the temperature of a solid is increased enough, it will become a liquid
When temperature is increased even more, it becomes a gas.

3. Phase Changes
To change phase, we must add or remove ENERGY in the form of heat
When adding heat energy…
If phase DOES NOT change, temperature and KE increase
If phase DOES change, temperature remains constant and PE increases

4. Phase Change and Temperature
Heat transferred during a change of state doesn't change the temperature.

5. Concept Check When adding heat energy… When does temperature increase?
When does temperature remain constant?

6. Thermal Energy

7. Kinetic Theory What is the kinetic theory of matter?
Kinetic theory explains the behavior of solids, liquids, and gases.
ALL particles of matter are in constant random motion.
We don’t observe the movement directly, but we can measure it indirectly
Pressure and temperature (macroscopic) are indicators of particle movement (microscopic)

8. Kinetic Theory: “big indicates little”
Macroscopic properties: big, easy to observe
(like temperature and pressure)
Microscopic properties: small, difficult to observe
(like motion, velocity, and momentum of atoms)

9. Temperature The measure of an object’s average kinetic energy.
how hot or cold something is, with respect to a standard (temperature scale – ⁰F, ⁰C, or K))
Measured with a thermometer

10. Temperature and Molecular Kinetic Energy
All the particles in a given object have different KE’s.
Temperature measures the average KE of all the particles in an object.
So…
Higher KE = Higher Temperature
Lower KE = Lower Temperature

11. Temperature Scales and Water
Celsius Scale -
Freeze at 0⁰
Boil at 100⁰
Fahrenheit Scale –
Freeze at 32⁰
Boil at at 212o
Kelvin Scale –
Freeze at 273 K
Boil at 373 K
Freezing is freezing is freezing…
0 ⁰C = 32 ⁰F = 273 K
100 ⁰C = 212 ⁰F = 373 K

12. Concept Check
What is temperature?

13. Pressure
A measure of the force of particle collisions over the surface of a container
Pressure = Force/Area
P = F/A (units: N/m2)

14. Pressure and Molecular Kinetic Energy
Pressure increases when the average kinetic energy (temperature) of the particles increase
More KE means…
More velocity, and therefore more momentum
Particles hit with more force and are moving faster

15. Observations… As the volume changes: Describe how pressure changes
Describe how the motion of the molecules change

16. Concept Check
How are pressure and molecular motion related?

17. Heat
Heat is the amount of energy transferred between two objects as a result of differences in temperature
represented by “Q”
Measured in Joules (J) or calories (c)
Direction of energy flow is always from hot to cold
+Q – heat has been absorbed (gained)
- Q – heat has been lost

18. Thermal Equilibrium
Thermal energy transfers between two objects until the reach the same temperature
Thermal equilibrium occurs when the average kinetic energy of the atoms and molecules is the same

19. Specific Heat
When heat flows into an object, thermal energy increases, increasing the temperature
Increase depends on the material and its mass
Different materials require different amounts of heat to change temperature

20. Specific Heat
The amount of energy that must be added to a material to raise the temperature of a unit mass of the material by one unit temperature
Measured in J/g●K or J/g●ºC
Kelvin or Celsius, doesn’t matter… the magnitude of each degree is the same.

21. Concept Check
What is specific heat?

22. Happens in most solids, liquids & gases
Thermal Expansion
Increase in the size due to an increase in temperature
If temp then size
Happens in most solids, liquids & gases
Water is an exception – it expands
as it becomes a solid!

23. Thermal Expansion Materials expand when heated
Materials contract when cooled
Expansion joints
Ring sizes

24. Discuss & write…
Describe Use the kinetic theory of matter to describe the effect of cold winter weather on the air pressure inside a car tire.
Describe Cake batter and bread dough can “rise” dramatically during baking. Use the kinetic theory of matter to describe one way in which the heat of an oven can help to produce this increase in size.
Describe Use the kinetic theory of matter to describe why the high specific heat of water makes it an ideal substance for thawing frozen food or for cooling down overheating machinery.

25. Calculating Heat Changes
Q = mc∆T
Q = heat gained(+) or lost(-)
m = mass (g)
c = specific heat of material (J/g●K or J/g●ºC)
∆T = temperature change (K or ºC)
IMPORTANT: Notice that mass is measured in GRAMS!!!!!

26. Example 1
How much heat is absorbed by 60 g of copper (c = J/gºC) when its temperature is raised from 20ºC to 80ºC ?
ANS: J

27. Example 2
A child is given a 175 g silver spoon which she promptly puts in her mouth. The spoon was initially at room temperature (20°C) and the child’s mouth is 37°C. If 684 Joules of energy is gained by the spoon, what is the specific heat of silver?

28. Law of Heat Exchange Remember the Law of Conservation of Energy
The sum of heat loss and heat gain in a closed system is zero.
When 2 bodies of unequal temp. are mixed, the cold body absorbs heat from the warm body (loses heat) until an equilibrium temperature is reached.
Qloss + Qgain = O

29. Example 3
If 30 grams of water (c = 1 cal/g°C) at 12⁰C is mixed with 80 grams of water at 88 ⁰C , what will the final temperature be?

30. Heat Transfer & Thermodynamics
Chapters 22 & 24

31. Conduction
Conduction is explained by collisions between atoms or molecules, and the actions of loosely bound electrons.
When the end of an iron rod is held in a flame, the atoms at the heated end vibrate more rapidly.
These atoms vibrate against neighboring atoms.
Free electrons that can drift through the metal jostle and transfer energy by colliding with atoms and other electrons.

32. Convection occurs in all fluids, liquid or gas.
When the fluid is heated, it expands, becomes less dense, and rises.
Cooler fluid then moves to the bottom, and the process continues.
In this way, convection currents keep a fluid stirred up as it heats.

33. How does the sun warm Earth’s surface?
Radiation
How does the sun warm Earth’s surface?
It can’t be through conduction or convection, because there is nothing between Earth and the sun.
The sun’s heat is transmitted by another process.
Radiation is energy transmitted by electromagnetic waves. Radiation from the sun is primarily light.

34. Heat Transfer

35. First Law of Thermodynamics
The net heat put into a system is equal to the change in internal energy of the system plus the work done by the system.
Basically, the Law of Conservation of Energy restated.

36. First Law of Thermodynamics
If we add heat energy to a system, the added energy does one or both of two things:
increases the internal energy of the system if it remains in the system
does external work if it leaves the system
So, the first law of thermodynamics states:
Heat added = increase in internal energy + external work done by the system

37. First Law of Thermodynamics
James Joule’s Paddle Wheel Apparatus
As the weights fall, they give up potential energy and warm the water accordingly. This was first demonstrated by James Joule, for whom the unit of energy is named.

38. First Law of Thermodynamics
Q = U + W
Q = Heat added to a system
U = Increase in internal energy
W = Work done by (+) or on (-) the system
Always measured in Joules

39. Example
A quantity of gas in a cylinder receives 1200J of heat from a hot plate. At the same time 600J of work are done on the gas by outside forces pressing down on a piston. Calculate the change in internal energy of the gas.

40. Second Law of Thermodynamics
Natural processes go in a direction that maintains or increases the total entropy of the universe.
Recall: Entropy –
Measure of disorder; the more entropy, the higher the temperature.
Simply, heat flows from high to low temperature

41. Heat Engines
When heat energy flows in any heat engine from a high-temperature place to a low-temperature place, part of this energy is transformed into work output.

42. Entropy Entropy is the measure of the amount of disorder in a system.
Disorder increases; entropy increases.

43. Entropy
Gas molecules escaping from a bottle move from a relatively orderly state to a disorderly state.
Organized structures in time become disorganized messes. Things left to themselves run down.
When a physical system can distribute its energy freely, entropy increases and energy of the system available for work decreases.

44. Entropy The laws of thermodynamics are sometimes put this way:
You can’t win (because you can’t get any more energy out of a system than you put in).
You can’t break even (because you can’t even get as much energy out as you put in).
You can’t get out of the game (entropy in the universe is always increasing).

45. Absolute Zero
A theoretical temperature at which no further thermal energy can be removed from an object
Usually shown as -273ºC or 0 K
Kelvin Scale is based on Absolute zero
“No system can reach absolute zero” – Third Law of Thermodynamics

46. Absolute Zero
The absolute temperatures of various objects and phenomena.