3
Physics HE 101: Lecture 23 Temperature and Ideal Gas
q Today's
lecture will cover Textbook Chapter 13.1-13.4
Physics 101: Lecture 23, Pg 1
Internal Energy and Temperature
q
All objects have "internal energy" (measured in Joules)
random motion of molecules kinetic energy collisions of molecules gives rise to pressure
q
Amount of internal energy depends on
temperature related to average kinetic energy per molecule how many molecules mass "specific heat" related to how many different ways a molecule can move
s s s
translation rotation vibration
the more ways it can move, the higher the specific heat
Physics 101: Lecture 23, Pg 2
10
Zeroth law of Thermodynamics
q If
two objects are in thermo equilibrium with a third, then the two are in equilibrium with each other. they are in equilibrium, they are at the same temperature
q If
Physics 101: Lecture 23, Pg 3
12
Can you tell Temperature
q NO
q Need
Thermometers
Physics 101: Lecture 23, Pg 4
15
Temperature Scales
Fare it nhe
212 100
C lcius e
Ke lvin
373.15 Wate boils r
32
0
273.15
Wate fre ze r e s
9 F = C + 32 5 K = C + 273
C=
5 ( F - 32) 9 C = K - 273
Physics 101: Lecture 23, Pg 5
14
NOTE: K=0 is "absoluteze m aning (alm ze KE/m cule ro", e ost) ro ole
Sick Act
You measure your body temperature with a thermometer calibrated in degrees Kelvin. What do you hope the reading is (assuming you are not trying to fake some sort of illness) ? F = 98.6 A. 307 K 5 corre ct B. 310 K C = (F - 32) = 37 9 C. 313 K K = C + 273 = 310 D. 317 K
Physics 101: Lecture 23, Pg 6
17
Temp Scales ACT
q Two
cups of coffee are heated to 100 degrees Fahrenheit. Cup 1 is then heated an additional 20 degrees Centigrade, cup 2 is heated an additional 20 Kelvin. Which cup of coffee is hotter?
A) One
B) Two
C) Same
K = C + 273
Physics 101: Lecture 23, Pg 7
20
Thermal Expansion
q When
temperature rises
molecules have more kinetic energy they are moving faster, on the average consequently, things tend to expand
q amount
of expansion depends on...
Te p: T m L0 L Te p: T+T m
change in temperature original length
coefficient of thermal expansion L0 + L = L0 + L0 T L = L0 T (linear expansion) V = V0 T (volume expansion)
Physics 101: Lecture 23, Pg 8
23
Clicker Test!
q Your
participation for this lecture will be determined by how you answer the next 3 questions! You can vote only once, so watch your green light carefully! and wait until I say "GO"
Physics 101: Lecture 23, Pg 9
CC 1
q Vote
A (once and only once!)
Physics 101: Lecture 23, Pg 10
CC 2
q Vote
D (once and only once!)
Physics 101: Lecture 23, Pg 11
CC 3
q Vote
B (once and only once!)
Physics 101: Lecture 23, Pg 12
Density ACT
As you heat a block of aluminum from 0 C to 100 C its density A. Increases C ORREC T B. Decreases T = 100 C C. Stays the same T= 0C
M, V0 0 = M / V0
M, V100 100 = M / V100 < 0
Physics 101: Lecture 23, Pg 13
26
Differential Expansion ACT
qA
bimetallic strip is made with aluminum =16x10-6 /K on the left, and iron =12x10-6 /K on the right. At room temperature, the lengths of metal are equal. If you heat the strips up, what will it look like?
Alum inumge longe force curveso its on outside ts r, s
A
B
C
Physics 101: Lecture 23, Pg 14
29
Amazing Water
q Water
is very unusual in that it has a maximum density at 4 degrees C. That is why ice floats, and exist!
1000.00 we 999.95 999.90 999.85 999.80 999.75 999.70 999.65 999.60 999.55 0 2 4 6 8 10
Density
Physics 101: Lecture 23, Pg 15
30
Swimming Preflight
Not being a great athlete, and having lots of money to spend, Gill Bates decides to keep the lake in his back yard at the exact temperature which will maximize the buoyant force on him when he swims. Which of the following would be the best choice? 1000.00 A. 0 C 999.95 B. 4 C C ORRECT 999.90 999.85 C. 32 C 999.80 D. 100 C 999.75 FB = lVg 999.70 E. 212 C
999.65 999.60 999.55
Density
0
2
4
6
8
10
Theanswe is 4 C be r , causewate has its gre st de r ate nsity at 4 C . S bouyant forceis e ince qual to thewe of thedisplace fluid or ight d de nsity*volum , whe thede e n nsity is thelarge thebouyant force st, is m ize axim d.
Physics 101: Lecture 23, Pg 16
32
Tight Fit
An aluminum plate has a circular hole cut in it. An aluminum ball (solid sphere) has exactly the same diameter as the hole when both are at room temperature, and hence can just barely be pushed through it. If both the plate and the ball are now heated up to a few hundred degrees Celsius, how will the ball and the hole fit ? A. The ball wont fit through the hole any more B. The ball will fit more easily through the hole C. Same as at room temperature C ORREC T
Theball ge large but so doe thehole S the havethe ts r, s ! ince y sam e e xpansion rate e rything will stay thesam ! , ve e
Physics 101: Lecture 23, Pg 17
35
Why does the hole get bigger when the plate expands ???
Im aginea platem from9 sm r pie s. ade alle ce Each pie e ce xpands. I f you re oveonepie , it will le an "e m ce ave xpande hole d "
Obje at te p T ct m
S eobje at hige T: am ct r Plateand holeboth ge large t r
Physics 101: Lecture 23, Pg 18
36
Stuck Lid Act
A glass jar ( = 3x10-6 K-1) has a metal lid ( = 16x10-6 K-1) which is stuck. If you heat them by placing them in hot water, the lid will be C ORREC T A. Easier to open B. Harder to open C. Same
C r lid e oppe xpands m , m ore aking a loose r fit, and e r ...