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The container on the left is cooler, the molecules move
slower (have less kinetic energy) and exert a smaller
pressure on the container walls compared to the molecules
of the warmer container at right.
Boiling:
100 oC
373 K
212 oF
Freezing:
0 oC
273 K
32 oF
A temperature change of 1oC
is the same as a temperature
change of 1 K. Both of these
are equal to a temperature
change of 1.8 oF.
1 calorie is the amount of heat
energy needed to raise 1.0 gram of
water by 1.0 oC.
1 calories is the amount of heat energy needed to raise 1.0 gram of water by 1.0 oC.
How much energy is need to raise 10 gm of water by 1.0 oC?
How much energy is need to raise 5 gm of water by 1.0 oC?
How much energy is need to raise 5 gm of water by 3.0 oC?
How much energy is need to raise 10 gm of water by 1.0 oC? 10 calories
How much energy is need to raise 5 gm of water by 1.0 oC? 5 calories
How much energy is need to raise 5 gm of water by 3.0 oC? 15 calories
The heat capacity of an object is the total amount of heat energy needed to raise the temperature
of an object by 1.0 oC
The heat capacity of the ocean is huge and the heat capacity of a cup of coffee is small. The heat
capacity of 10 gm of water is 10 calories/oC and that of 5 grams of water is 5 calorie/oC.
Heat capacity is also called thermal inertia as it describes how hard it is to change an object’s
temperature.
1 calorie is the amount of heat
energy needed to raise 1.0 gram of
water by 1.0 oC.
The specific heat capacity of water
is 1.0 calorie/gm/oC
The amount of heat energy required
to raise 1.0 gm of rock by 1.0 oC is
about 0.2 calories so the specific
heat capacity of rock is only 0.2
calorie/gm/oC.
Water has one of the highest specific heat capacities of normal substances. This makes it an
excellent medium for storing solar energy. The idea is that it is hard to store heat energy in a
material if the material gets hot. So, since water can hold a lot of energy (High heat capacity)
without getting very hot, it is a perfect storage medium.
Table 2-1, p. 30
Object A has a large heat capacity relative to object B .
(Circle any of the correct statements)
1. For a given energy input, the temperature of object A
will increase more than that of object B.
2. For a given energy loss, the temperature of object A will
drop less than that of object B.
3. When both experience the same temperature increase the
energy input into A is larger.
Object A has a large heat capacity relative to object B .
(Circle any of the correct statements)
1. For a given energy input, the temperature of object A
will increase more than that of object B.
2. For a given energy loss, the temperature of object A will
drop less than that of object B.
3. When both experience the same temperature increase the
energy input into A is larger.
2 and 3 are correct statements
States of Matter
1. Gas
2. Liquid
3. Solid
Molecules of a gas have a high average energy compared
to molecules of a liquid or solid.
Molecules of a liquid have an intermediate average energy
compared to molecules of a gas or solid.
Molecules of a soli have the lowest average energy
compared to molecules of a liquid or gas.
It takes energy to convert ice into liquid water. That is it takes energy
to melt ice. As ice in an ice water mixture melts the temperature
doesn’t change. All of the energy going into the ice water id used to
change ice into water. This energy is referred to as latent heat energy.
Latent means hidden .
It takes energy to liquid water in water vapor. The Latent heat for
evaporation comes from the environment. For example when you get
out of the pool on a nice day you are likely to get goose bumps on
your skin as water evaporates from your skin. Much of the latent
energy needed for evaporation comes from your skin.
For this reason evaporation is said to be a cooling process.
Sublimation is the process by which solid turns directly into vapor.
As frost disappears on a cold day (less than 32 oF) in Eastern WA it is
sublimating.
The opposite of sublimation is deposition; vapor turning directly into
ice like when frost forms.
As vapor condenses into liquid, energy is released into the
environment. As cloud drop form the surrounding air actually warms.
This release of latent heat energy into the environment via
condensation is a fundamental energy source of hurricanes and
thunderstorms. Snow formation and depositon also warm the
surrounding environment.
When water evaporates from your body, energy is
removed from or added to the water?
When water evaporates from your body, energy is
removed from or added to your body?
When water freezes energy is removed from or added to
the water?
When water evaporates from your body, energy is
removed from or added to the water?
When water evaporates from your body, energy is
removed from or added to your body?
When water freezes energy is removed from or added to
the water?
The energy released into the environment as clouds form
causes the air to warm which further enhance the vertical
growth of clouds.
3 mechanisms for Heat Transfer
1. Conduction
2. Convection
3. Radiation
Conduction: The energetic hot
molecules collide with less
energetic cooler molecules
transferring energy fro hot to
cold via molecular collisions.
Conduction through a wall, window, or slab of ice on a lake or ocean.
Relative Thermal Conductivities
Silver
Aluminum
Water
Snow
Ice
Wood
420
240
0.57
0.20
2.2
0.15
Vacuum
0.0
Convection is the transfer of energy from hot to cold via the net flow of
warm fluid (liquid or gas). In meteorology vertical air motion and heat
transfer it referred to as convection and horizontal flow is advection.
Thermal convection developing in the afternoon cools
the ground and warms the air above.
As air rises it expands because the pressure it feel gets smaller and
smaller. Expanding air naturally cools. Try this! Open your mouth
fairly wide and gently blow air onto your hand. It will likely feel warm.
Now pucker and blow air rapidly onto you hand through a small opening
in your mouth. It should feel a bit cooler.
The freezer compartment becomes very cold as the
refrigeration fluid escapes through the expansion valve.
As air sinks it is compressed because the pressure it feel gets greater and
greater. Compressed air naturally warms. Try this! Feel the bottom of
your bicycle pump after you have been pumping air into your tire.
As the air filled tube is compressed the tissue paper ignites.
In a diesel engine as the air fuel mixture is compressed rapidly it
ignites. No need for spark plugs, rapid compression is enough to
keep the engine running.
Expanding (rising) air cools
Compressing (sinking) air warms
Newton’s Law of cooling
Hot objects lose heat energy Faster
than Warm objects
Newton’s law of cooling applies to all
three forms of heat transfer.
A cooling cup of coffee
Newton’s law of cooling states that a cup of coffee cools
of fast initially and then more gradually as it approaches
room temperature.
A cup of coffee cools from 90°F to 80°F in 1.0 minute. If the
same coffee starts out at 180 °F how long will it take to cool to
170 °F? a) More than 1 minute b) Less than 1 minute c)
about 1 minute
A cup of coffee cools from 90°F to 80°F in 1.0 minute. If the
same coffee starts out at 180 °F how long will it take to cool to
170 °F? a) More than 1 minute b) Less than 1 minute c)
about 1 minute