13.1 Degrees
Which is the largest unit: one
Celsius degree, one Kelvin
degree, or one Fahrenheit
degree?
1) one Celsius degree
2) one Kelvin degree
3) one Fahrenheit degree
4) both one Celsius degree and
one Kelvin degree
5) both one Fahrenheit degree
and one Celsius degree
13.1 Degrees
Which is the largest unit: one
Celsius degree, one Kelvin
degree, or one Fahrenheit
degree?
1) one Celsius degree
2) one Kelvin degree
3) one Fahrenheit degree
4) both one Celsius degree and
one Kelvin degree
5) both one Fahrenheit degree
and one Celsius degree
The Celsius degree and the Kelvin degree are the same size. The
scales only differ by an offset, not by the size of the degree unit. For
Fahrenheit, there are 180 degrees between boiling and freezing
(212°F–32°F). For Celsius, there are 100 degrees between the same
points, so the Celsius (and Kelvin) degrees must be larger.
13.2 Freezing Cold
It turns out that – 40°C is the same
temperature as – 40°F. Is there a
temperature at which the Kelvin and
Celsius scales agree?
1) yes, at 0 °C
2) yes, at -273 °C
3) yes, at 0 K
4) no
13.2 Freezing Cold
It turns out that – 40°C is the same
temperature as – 40°F. Is there a
temperature at which the Kelvin and
Celsius scales agree?
1) yes, at 0 °C
2) yes, at -273 °C
3) yes, at 0 K
4) no
The Celsius and Kelvin scales differ only by an offset, which is 273
degrees. Therefore, a temperature on one scale can never match the
same numerical value on the other scale. The reason that such
agreement is possible for Celsius and Fahrenheit is the fact that the
actual degree units have different sizes (recall the previous question).
13.4 Glasses
1) run hot water over them both
Two drinking glasses are
stuck, one inside the other.
How would you get them
unstuck?
2) put hot water in the inner one
3) run hot water over the outer one
4) run cold water over them both
5) break the glasses
13.4 Glasses
1) run hot water over them both
Two drinking glasses are
stuck, one inside the other.
How would you get them
unstuck?
2) put hot water in the inner one
3) run hot water over the outer one
4) run cold water over them both
5) break the glasses
Running hot water only over the outer glass will
allow the outer one to expand, while the inner glass
remains relatively unchanged. This should loosen
the outer glass and free it.
13.5a
Steel Expansion I
A steel tape measure is
marked such that it gives
accurate length measurements 1) measured lengths will be too small
at room temperature. If the
2) measured lengths will still be accurate
tape measure is used outside
on a very hot day, how will its 3) measured lengths will be too big
length measurements be
affected?
13.5a
Steel Expansion I
A steel tape measure is
marked such that it gives
accurate length measurements 1) measured lengths will be too small
at room temperature. If the
2) measured lengths will still be accurate
tape measure is used outside
on a very hot day, how will its 3) measured lengths will be too big
length measurements be
affected?
The tape measure will expand, so its markings will spread out
farther than the correct amount. When it is laid down next to an
object of fixed length, you will read too few markings for that given
length, so the measured length will be too small.
13.5b
Steel Expansion II
Metals such as brass expand when
heated. The thin brass plate in the
movie has a circular hole in its
center. When the plate is heated,
what will happen to the hole?
1) gets larger
2) gets smaller
3) stays the same
4) vanishes
13.5b
Steel Expansion II
Metals such as brass expand when
heated. The thin brass plate in the
movie has a circular hole in its
center. When the plate is heated,
what will happen to the hole?
1) gets larger
2) gets smaller
3) stays the same
4) vanishes
Imagine drawing a circle on the
plate. This circle will expand
outward along with the rest of the
plate. Now replace the circle with
the hole, and you can see that the
hole will expand outward as well.
Note that the material does NOT
“expand inward” to fill the hole!!
expansion
14.1a
Two objects are made of
the same material, but have
different masses and
temperatures. If the
objects are brought into
thermal contact, which one
will have the greater
temperature change?
Thermal Contact I
1) the one with the higher initial temperature
2) the one with the lower initial temperature
3) the one with the greater mass
4) the one with the smaller mass
5) the one with the higher specific heat
14.1a
Two objects are made of
the same material, but have
different masses and
temperatures. If the
objects are brought into
thermal contact, which one
will have the greater
temperature change?
Thermal Contact I
1) the one with the higher initial temperature
2) the one with the lower initial temperature
3) the one with the greater mass
4) the one with the smaller mass
5) the one with the higher specific heat
Since the objects are made of the same material, the only difference
between them is their mass. Clearly, the object with less mass will be
much easier to change temperature since there is not much material
there (compared to the more massive object).
14.2 Two Liquids
Two equal-mass liquids, initially at the
same temperature, are heated for the same
1) the cooler one
time over the same stove. You measure
2) the hotter one
the temperatures and find that one liquid
has a higher temperature than the other.
Which liquid has a higher specific heat?
3) both the same
14.2 Two Liquids
Two equal-mass liquids, initially at the
same temperature, are heated for the same
1) the cooler one
time over the same stove. You measure
2) the hotter one
the temperatures and find that one liquid
has a higher temperature than the other.
3) both the same
Which liquid has a higher specific heat?
Both liquids had the same increase in internal energy,
because the same heat was added.
But the cooler liquid
had a lower temperature change.
Since Q = mcDT, if Q and m are both the same and DT is
smaller, then c (specific heat) must be bigger.
14.3a
Night on the Field
The specific heat of concrete is
greater than that of soil. A baseball
field (with real soil) and the
surrounding parking lot are warmed
up during a sunny day. Which would
you expect to cool off faster in the
evening when the sun goes down?
1) the concrete parking lot
2) the baseball field
3) both cool off equally fast
14.3a
Night on the Field
The specific heat of concrete is
greater than that of soil. A baseball
field (with real soil) and the
surrounding parking lot are warmed
up during a sunny day. Which would
you expect to cool off faster in the
evening when the sun goes down?
1) the concrete parking lot
2) the baseball field
3) both cool off equally fast
The baseball field, with the lower specific heat, will change
temperature more readily, so it will cool off faster. The high specific
heat of concrete allows it to “retain heat” better and so it will not cool
off so quickly – it has a higher “thermal inertia.”
14.4 Calorimetry
1) 0 oC
1 kg of water at 100 oC is poured into a
2) 20 oC
bucket that contains 4 kg of water at 0
3) 50 oC
oC.
4) 80 oC
Find the equilibrium temperature
(neglect the influence of the bucket).
5) 100 oC
14.4 Calorimetry
1) 0 oC
1 kg of water at 100 oC is poured into a
2) 20 oC
bucket that contains 4 kg of water at 0
3) 50 oC
oC.
4) 80 oC
Find the equilibrium temperature
(neglect the influence of the bucket).
Since the cold water mass is greater, it will
have a smaller temperature change!
5) 100 oC
Q1 = Q2
The masses of cold/hot have a ratio of 4:1,
m1cDT1 = m2cDT2
so the temperature change must have a
DT1 / DT2 = m2 / m1
ratio of 1:4 (cold/hot).
14.5 More Calorimetry
A 1 kg block of silver (c = 234 J/kg
0C
) is heated to 100 0C, then
1) 0oC
2) between 0oC and 50oC
dunked in a tub of 1 kg of water (c
3) 50oC
= 4186 J/kg 0C ) at 0 0C. What is the
4) between 50oC and 100oC
final equilibrium temperature?
5) 100oC
14.5 More Calorimetry
A 1 kg block of silver (c = 234 J/kg
0C
) is heated to 100 0C, then
1) 0oC
2) between 0oC and 50oC
dunked in a tub of 1 kg of water (c
3) 50oC
= 4186 J/kg 0C ) at 0 0C. What is the
4) between 50oC and 100oC
final equilibrium temperature?
5) 100oC
Since cwater >> csilver it takes more heat to
change the temperature of the water than it
Q1 = Q2
does to change the temperature of the silver.
mc1DT1 = mc2DT2
In other words, it is much “harder” to heat the
DT1 / DT2 = c2 / c1
water!! Thus, the final temperature has to be
closer to the initial temperature of the water.
14.6 Adding Heat
If you add some heat to a substance,
is it possible for the temperature of
the substance to remain unchanged?
1) yes
2) no
14.6 Adding Heat
If you add some heat to a substance,
is it possible for the temperature of
the substance to remain unchanged?
1) yes
2) no
Yes, it is indeed possible for the temperature to stay the same. This is
precisely what occurs during a phase change – the added heat goes
into changing the state of the substance (from solid to liquid or from
liquid to gas) and does not go into changing the temperature! Once
the phase change has been accomplished, then the temperature of the
substance will rise with more added heat.
14.7 Hot Potato
Will potatoes cook faster if the
water is boiling faster?
1) yes
2) no
14.7 Hot Potato
Will potatoes cook faster if the
water is boiling faster?
1) yes
2) no
The water boils at 100 °C and remains at that temperature until all
of the water has been changed into steam. Only then will the
steam increase in temperature. Since the water stays at the same
temperature, regardless of how fast it is boiling, the potatoes will
not cook any faster.
14.8 Water and Ice
You put 1 kg of ice at 0oC
together with 1 kg of water at
50oC. What is the final
temperature?
LF = 80 cal/g
cwater = 1 cal/g oC
1) 0oC
2) between 0oC and 50oC
3) 50oC
4) greater than 50oC
14.8 Water and Ice
You put 1 kg of ice at 0oC
together with 1 kg of water at
50oC. What is the final
temperature?
LF = 80 cal/g
cwater = 1 cal/g oC
1) 0oC
2) between 0oC and 50oC
3) 50oC
4) greater than 50oC
How much heat is needed to melt the ice?
Q = m Lf = (1000g)  (80 cal/g) = 80,000 cal
How much heat can the water deliver by cooling from 50oC to 0oC?
Q = cwater m DT = (1 cal/g oC)  (1000g)  (50oC) = 50,000 cal
Thus, there is not enough heat available to melt all the ice!!
14.9 Ice and Steam
You put 1 kg of ice at 0oC
together with 1 kg of steam at
1) between 0oC and 50oC
100oC. What is the final
2) 50oC
temperature?
3) between 50oC and 100oC
LF = 80 cal/g, Lv = 540 cal/g
cwater = 1 cal/g oC
4) 100oC
5) greater than 100oC
14.9 Ice and Steam
You put 1 kg of ice at 0oC
together with 1 kg of steam at
1) between 0oC and 50oC
100oC. What is the final
2) 50oC
temperature?
3) between 50oC and 100oC
LF = 80 cal/g, Lv = 540 cal/g
cwater = 1 cal/g oC
4) 100oC
5) greater than 100oC
How much heat is needed to melt the ice?
Q = m Lf = (1000g)  (80 cal/g) = 80,000 cal
How much heat is needed to raise the water temperature to 100oC?
Q = cwater m DT = (1 cal/g oC)(1000g)(100oC) = 100,000 cal
But if all of the steam turns into water, that would release 540,000 cal.
Thus, some steam is left over, and the whole mixture stays at 100oC.
14.12
Heat Conduction
Given your experience of
what feels colder when you
walk on it, which of the
surfaces would have the
highest thermal conductivity?
a)
b)
c)
d)
a rug
a steel surface
a concrete floor
has nothing to do with
thermal conductivity
14.12
Heat Conduction
Given your experience of
what feels colder when you
walk on it, which of the
surfaces would have the
highest thermal conductivity?
a)
b)
c)
d)
a rug
a steel surface
a concrete floor
has nothing to do with
thermal conductivity
All things being equal, bigger k leads to bigger
heat loss.
From the packet: Steel=50, Concrete=0.8,
Human body=0.17, Wool=0.04, in units of W/m*C0).
Three Containers
Three containers are filled with water to the same 1) container 1
height and have the same surface area at the
base, but the total weight of water is different for
each. Which container has the greatest total
force acting on its base?
2) container 2
3) container 3
4) all three are equal
Three Containers
Three containers are filled with water to the same 1) container 1
height and have the same surface area at the
base, but the total weight of water is different for
each. Which container has the greatest total
force acting on its base?
The pressure at the bottom of each
container depends only on the height
of water above it! This is the same for
all the containers. The total force is
the product of the pressure times the
area of the base, but since the base is
also the same for all containers, the
total force is the same.
2) container 2
3) container 3
4) all three are equal
The Straw I
1) water pressure
When you drink liquid through a
straw, which of the items listed
below is primarily responsible for
this to work?
2) gravity
3) inertia
4) atmospheric pressure
5) mass
The Straw I
1) water pressure
When you drink liquid through a
straw, which of the items listed
below is primarily responsible for
this to work?
2) gravity
3) inertia
4) atmospheric pressure
5) mass
When you suck on a straw, you expand your lungs, which
reduces the air pressure inside your mouth to less than
atmospheric pressure. Then the atmospheric pressure pushing
on the liquid in the glass provides a net upward force on the
liquid in the straw sufficient to push the liquid up the straw.
Wood in Water I
Two beakers are filled to the brim with water. A wooden block
is placed in the second beaker so it floats. (Some of the
water will overflow the beaker.) Both beakers are then
weighed. Which scale reads a larger weight?
same for both
Wood in Water I
Two beakers are filled to the brim with water. A wooden block
is placed in the second beaker so it floats. (Some of the
water will overflow the beaker.) Both beakers are then
weighed. Which scale reads a larger weight?
The block in B displaces an amount of
water equal to its weight, since it is
floating. That means that the weight
of the overflowed water is equal to the
weight of the block, and so the beaker
in B has the same weight as that in A.
same for both
Two Bricks
Imagine holding two identical
bricks in place under water.
Brick 1 is just beneath the
surface of the water, while brick 2
is held about 2 feet down. The
force needed to hold brick 2 in
place is:
1) greater
2) the same
3) smaller
1
2
Two Bricks
Imagine holding two identical
bricks in place under water.
Brick 1 is just beneath the
surface of the water, while brick 2
is held about 2 feet down. The
force needed to hold brick 2 in
place is:
1) greater
2) the same
3) smaller
The force needed to hold the brick in
place underwater is: W – FB. According
to Archimedes’ Principle, FB is equal to
the weight of the fluid displaced. Since
each brick displaces the same amount of
fluid, then FB is the same in both cases.
1
2
Archimedes I
An object floats in water with 3/4 of
its volume submerged. What is the
ratio of the density of the object to
that of water?
1) 1/4
2) 1/3
3) 4/3
4) 3/4
5) 2/1
10.12a
Archimedes I
An object floats in water with 3/4 of
its volume submerged. What is the
ratio of the density of the object to
3) 4/3
5) 2/1
Remember that we have:
Vobject
2) 1/3
4) 3/4
that of water?
V fluid
1) 1/4

object
 fluid
so if the ratio of the volume of the
displaced water to the volume of the
object is 3/4, the object has 3/4 the
density of water.
10.12b
Archimedes II
The object is now placed in oil
with a density half that of water.
What happens?
1) it floats just as before
2) it floats higher in the water
3) it floats lower in the water
4) it sinks to the bottom
10.12b
Archimedes II
The object is now placed in oil
with a density half that of water.
What happens?
1) it floats just as before
2) it floats higher in the water
3) it floats lower in the water
4) it sinks to the bottom
We know from before that the object has
3/4 the density of water. If the water is
now replaced with oil, which has 1/2 the
density of water, the density of the object
is larger than the density of the oil.
Therefore, it must sink to the bottom.
10.15a
Fluid Flow
Water flows through a 1-cm diameter pipe
(1) one quarter
connected to a 1/2-cm diameter pipe.
(2) one half
Compared to the speed of the water in the
(3) the same
1-cm pipe, the speed in the 1/2-cm pipe is:
(4) double
(5) four times
10.15a
Fluid Flow
Water flows through a 1-cm diameter pipe
(1) one quarter
connected to a 1/2-cm diameter pipe.
(2) one half
Compared to the speed of the water in the
(3) the same
1-cm pipe, the speed in the 1/2-cm pipe is:
(4) double
(5) four times
v1
v2
The area of the small pipe is less, so we know that the water will flow
faster there. Since A  r2, when the radius is reduced by 1/2, the area is
reduced by 1/4, so the speed must increase by 4 times to keep the flow
rate (A  v) constant.
On Golden Pond
A boat carrying a large chunk of
steel is floating on a lake. The
chunk is then thrown overboard and
sinks. What happens to the water
level in the lake?
1) rises
2) drops
3) remains the same
4) depends on the size
of the steel
On Golden Pond
A boat carrying a large chunk of
steel is floating on a lake. The
chunk is then thrown overboard and
sinks. What happens to the water
level in the lake
1) rises
2) drops
3) remains the same
4) depends on the size
of the steel
Initially the chunk of steel “floats” by
sitting in the boat. The buoyant force
is equal to the weight of the steel, and
this will require a lot of displaced water
to equal the weight of the steel. When
thrown overboard, the steel sinks and
only displaces its volume in water.
This is not so much water -- certainly
less than before -- and so the water
level in the lake will drop.