Again, try to name each phase change
and show the direction of energy flow (into or out of
the material) when the phase change occurs
You might not have heard of
deposition before when a gas changes directly to a
solid. The formation of frost is an example of
deposition.
You can consciously remove energy from water vapor to
make it condense. You take energy out of water to
cause it to freeze (you could put water in a
freezer; energy would flow from the relatively
warm water to the colder surroundings). If one of
these phase changes occurs, without you playing a role,
energy will be released into the surroundings (causing
the surroundings to warm).
Note the direction of the energy arrows - energy is
being released into the surroundings (warming the
surroundings). It's kind of like a genie coming
out of a magic lamp. One Scooby Wright worth of
kinetic energy is released when enough water freezes to
make an ice cube. Many Scooby Wrights are released
when water vapor condenses.
This release of energy into the
surroundings and the warming of the surroundings is a
little harder for us to appreciate because it never
really happens to us in a way that we can feel.
Have you ever stepped out of an air conditioned building
into warm moist air outdoors and had your glasses or
sunglasses "steam up"? Water vapor never condenses
onto your body (your body is too warm). However if
it did you would feel warm. It would be just the
opposite of the cold feeling when you step out of the
shower or a pool and the water on your body
evaporates. You know how cold the evaporation can
make you feel, the same amount of condensation would
produce a lot of warming. I suspect
we'd be surprised at how much warming it produces.
Alternate view
showing the latent heat energy in water vapor
and water coming out of hiding during a phase
change and being released into the surroundings.
Here's a practical application of what we have
been learning.
Cans of a cold drink are taken out of the
refrigerator and placed on the kitchen table on a
warm dry day and a warm humid day. Except
for the differences in the amount of moisture in
the air everything else is the same.
Moisture has condensed onto the can above at
right. Do the two cans warm up at the same
rate or does one warm up more quickly than the
other. In the latter case which can warms up
most rapidly.
The can on the right will warm more quickly.
Equal amounts of heat will flow from the warm air
into the cold cans in both cases. Condensation
of water vapor is an additional source of energy and
will warm that can more rapidly. I suspect
that the condensation may actually be the dominant
process.
The foam "cozy", "koozie",
or whatever you want to call it, that you can put
around a can of soda or beer is designed to insulate
the can from the warmer surroundings but also to
keep water vapor in the air from condensing onto the
can (source
of the image above)
We're beating this
concept to death but we're almost done. Two
more figures to illustrate how latent heat energy
transport can carry energy from location to
another.
1. You've just stepped out of
the shower and are covered with water. The water
is evaporating and energy is being taken from your
body.
2. The water vapor (containing latent heat energy,
the energy taken from your body), drifts into the
kitchen where it finds a cold can sitting on a
table.
3. Water vapor comes into contact with the cold
can and condenses. The hidden latent heat energy
in the water vapor is released into the can and warms
the drink inside.
Without you even
leaving the bathroom,
energy has effectively been transported from your
warm body to the cold can in the kitchen.
Here's what happens on a much grander scale in the
atmosphere.
We start in this picture in the tropics
where there is often a surplus of sunlight energy.
Some of the incoming sunlight evaporates ocean
water. The resulting water vapor moves somewhere
else and carries hidden latent heat energy with it. This
hidden energy reappears when something (air running into a
mountain and rising, expanding, and cooling) causes the
water vapor to condense. The condensation releases
energy into the surrounding atmosphere. This would
warm the air.
Energy arriving in sunlight in the tropics has
effectively been transported to the atmosphere in a place
like Tucson.
It's not clear how much time will be left in the period
at this point, but I've included a little additional
material nonetheless.
Energy transport by
electromagnetic radiation
It's time to tackle electromagnetic (EM)
radiation, the 4th and most important of the energy
transport processes.
Many introductory textbooks depict EM
radiation with a wavy line like shown above. They
don't usually explain what the wavy line represents.
The wavy line just connects the tips
of a bunch of "electric field arrows". But what exactly
are electric field arrows?
Static electricity and electric fields
To understand
electric fields we need to first step back and
review a couple of rules concerning static
electricity.
That won't take too long,
static electricity is something you're most likely
already familiar with.
Believe it or not there is even a National Static
Electricity Day (Jan. 9).
The
static electricity rules are found at the top of
p. 59 in the photocopied ClassNotes
Two electrical charges with the same polarity (two
positive charges or two negative charges) push each other
apart. Opposite charges are attracted to each other.
Here
are some pictures I found online.

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This girl became charged with
static electricity while jumping on a trampoline
and illustrates the repulsive force of like
charges. Her hair and body are all
charged up with charge of the same polarity.
We don't know what polarity it is.
The charge on her hair is trying to get as far
away from charge on her body. People's
hair will sometimes stand on end under a
thunderstorm. That is a very dangerous
situation to be in.
This photo was a National Geographic
Magazine 2013 Photo Contest winner (source)
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A cat covered in Styrofoam
"peanuts". Here the cat and the
"peanuts" have opposite charges and are
attracted to each other.
Being a cat owner I would worry about the
cat swallowing one of the peanuts and possibly
choking. (source)
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