1. Chapter 16. Temperature and Expansion
A PowerPoint Presentation by
Paul E. Tippens, Professor of Physics
Southern Polytechnic State University
© 2007

2. Internal energy -- spring analogies are helpful:
Thermal Energy
Thermal energy is the total internal energy of an object: the sum of its molecular kinetic and potential energies.
Thermal energy = U + K
Internal energy -- spring analogies are helpful:
U = ½kx2
K = ½mv2

3. Temperature
Temperature is related to the kinetic activity of the molecules, whereas expansion and phase changes of substances are more related to potential energy.
Although not true in all cases, a good beginning is to define temperature as the average kinetic energy per molecule.

4. Temperature vs. Internal Energy
The large pitcher and the small one have the same temperature, but they do not have the same thermal energy. A larger quantity of hot water melts more of the ice.

5. Temperature Equilibrium
Heat is defined as the transfer of thermal energy that is due to a difference in temperature.
Thermal Equilibrium
Hot Coals
Insulated Container
Two objects are in thermal equilibrium if and only if they have the same temperature.
Cool Water
Same Temperature

6. Zeroth Law of Thermodynamics
The Zeroth Law of Thermodynamics: If two objects A and B are separately in equilibrium with a third object C, then objects A and B are in thermal equilibrium with each other. A
Object C A B
Thermal Equilibrium
Same Temperature B
Object C

7. Temperature Scales
1000C
2120F
00C
320F
The lower fixed point is the ice point, the temperature at which ice and water coexist at 1 atm of pressure:
00C or 320F
The upper fixed point is the steam point, the temperature at which steam and water coexist at 1 atm of pressure:
1000C or F

8. Temperature Labels Dt = 600C – 200C Dt = 40 C0
If an object undergoes a change of temperature, we place the degree symbol 0 after the scale (C0 or F0) to indicate the interval of temperature.
ti = 600C
tf = 200C
Dt = 600C – 200C
Dt = 40 C0
We say: “The temperature decreases by forty Celsius degrees.”

9. Specific Temperatures
Same temperatures have different numbers: 0C 0F
2120F
320F
1000C
00C
180 F0
100 C0 tC tF

10. Convert 1600F to 0C from formula:
Example 1: A plate of food cools from 1600F to 650F. What was the initial temperature in degrees Celsius? What is the change in temperature in Celsius degrees?
Convert 1600F to 0C from formula:
tC = 71.10C
9 F0 = 5 C0
Dt = 52.8 C0

11. Comparison of Three Scales
1 C0 = 1 K
1000C
00C
-2730C
Celsius C
273 K
373 K
Kelvin
0 K K
Fahrenheit
320F
-4600F
2120F F
ice
steam
5 C0 = 9 F
Absolute zero
TK = tC

12. Linear Expansion to t Copper:  = 1.7 x 10-5/C0Lo L to t
Copper:  = 1.7 x 10-5/C0
Concrete:  = 0.9 x 10-5/C0
Iron:  = 1.2 x 10-5/C0
Aluminum:  = 2.4 x 10-5/C0

13. DL = aLoDt = (1.7 x 10-5/C0)(90 m)(80 C0)
Example 2: A copper pipe is 90 m long at 200C. What is its new length when steam passes through the pipe at 1000C?
Lo = 90 m, t0= 200C
Dt = 1000C - 200C = 80 C0
DL = aLoDt = (1.7 x 10-5/C0)(90 m)(80 C0)
DL = m
L = Lo + DL
L = 90 m m
L = m

14. Applications of Expansion
Expansion Joints
Bimetallic Strip
Brass
Iron
Expansion joints are necessary to allow concrete to expand, and bimetallic strips can be used for thermostats or to open and close circuits.

15. Area Expansion Expansion on heating. A0 A
Area expansion is analogous to the enlargement of a photograph.
Example shows heated nut that shrinks to a tight fit after cooling down.

16. Summary
Thermal energy is the total internal energy of an object: the sum of its molecular kinetic and potential energies.
Thermal energy = U + K
The Zeroth Law of Thermodynamics: If two objects A and B are separately in equilibrium with a third object C, then objects A and B are in thermal equilibrium with each other. A B
Thermal Equilibrium A
Object C B

17. Summary: Expansion Linear Expansion: to t Area Expansion: DA = 2aA0 DtLo L to t
DA = 2aA0 Dt
Area Expansion:
Expansion A0 A