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TOUCH THE CLOUDS William Beaty
2/96
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WARNING: ALWAYS EMPTY THE TANK AND THE RESEVOIR BETWEEN USES!
This device turns water into microscopic droplets which then
evaporate. If you allow bacteria to grow in the water, you
will soon be breathing invisible clouds of bacteria in the air!
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This device generates a pool of fog which resembles dry-ice fog, but uses
only water and air. Touch the pool and you touch cloud-stuff. Totally
fascinating to play with.
Needed:
- Ultrasonic Humidifier
- Aluminum foil
- Rubber band
Obtain a "Cool Mist" Ultrasonic Humidifier, about $60US, or $5 at garage
sales. These are the aquarium-shaped humidifiers which have a rectangular
water tank, and which eject cold steam from a spout at the top. Look for
them in larger drugstores. Lately they have become hard to find, possibly
because the danger associated with using them with polluted water.
Open up the humidifier's water-well where the float switch and ultrasonic
transducer reside. Here there will be an air tube jutting upwards from
the base which normally supplies the air flow to blow the mist out the
top. Cover this air outlet with aluminum foil and a rubber band. Now
poke a 1/2cm hole in the foil, the object being to vastly reduce the flow
without stopping it entirely. (Smaller holes will give more dense mist,
but with less rate of flow.) If you now resassemble the humidifier, and
turn it on to a high setting, you will find that a pool of white fog will
fill up and overflow the top. This "fluid" is composed of suspended water
droplets. It is not vapor, it is mist. It is the same substance as that
which makes up clouds. You can catch this mist in a dark-painted bowl,
fill cups with it and pour it on the table, fill cardboard tubes and blow
out a blast, make smoke rings, use it in a tornado machine, etc.
If you are ambitious, you can arrange a constantly-filled bowl of mist for
the kids to play with. Obtain a large plastic bowl. Paint the interior
black for contrast. Cut a fairly large hole in the bottom, or drill
numerous smaller holes, then cement the bowl over the hole on the top of
the humidifier with silicon caulk. You might also put some screening
across the hole(s), so small objects do not find their way into the water.
You'll find that the humidifier can be adjusted for fast-filling but
dilute fog, or for slow-filling dense fog which is as opaque as milk.
If you prefer not to modify your humidifer, you can build a different
version. Find a piece of white plastic pipe which you can jam securely
into the circular outlet at the top of the humidifier. Jam the pipe in,
mark where it passes out of the humidifier, then make another mark 1"
farther out. Cut the pipe off at this mark. Use this piece of pipe to
draw a circle on the bottom of your plastic bowl. Cut out the circle
along the mark. Jam the pipe into the humidifer, jam the bowl onto the
pipe, then use RTV silicone caulk (smells like vinegar) to securely seal
the pipe into the bowl. After the caulk hardens overnight, paint the
inside of the bowl black with oil paint or spray paint, and maybe glue a
piece of plastic window screen across the pipe to prevent nasty stuff from
finding its way into the water.
WARNING: ALWAYS EMPTY THE TANK AND THE RESEVOIR BETWEEN USES! ALWAYS USE
CLEAN, FRESH TAP WATER OR BOTTLED WATER.
WARNING: Ultrasonic Humidifiers break water into small drops. They do not
boil and recondense water as teakettles do. Therefore, if the water is
not clean, the device will spread the contamination into the air where it
will be inhaled. The mist droplets will evaporate and leave invisible
clouds of material in the air. If bacteria are allowed to grow in the
standing pool of water, they will be inhaled by everyone in the room. It
follows that it's a bad idea to use any liquid but water in the tank,
since it will be dispersed into the air and inhaled. (No, adding dye to
the water does not color the mist, but it might stain anything the mist
touches!)
Notes:
If you use soap to wash down the humidifier parts, rinse it very well
afterwards. A small amount of soap in the water will change the surface
tension and inhibit the mist production. If your device mysteriously
stops making mist, try cleaning out the humidifier's water-pool section
with non-soapy paper towels. As an experiment, drip some liquid soap into
the operating humidifier to see what happens.
Position the device away from drafts, as these will disturb the mist and
empty the bowl. If drafts cannot be avoided, use a smaller hole in the
aluminum foil plug, so that the mist will be heavier and less prone to
drafts (but the device will produce less mist and refill more slowly.)
If your device does not work well, let it run for five minutes and see if
it improves. Tiny amounts of oil or soap on the water surface will slow
down mist production, but will be eliminated in a few minutes.
Question:
This air/droplet "fluid" is quite dense, yet it is the same stuff as
clouds and fog. Why do clouds stay up? Why does fog hug the ground? The
answer is below(1), but it might present a topic of considerable
discussion for your kids.
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DEMONSTRATIONS:
Fill a cup with mist. Pour it over someone's head. Pour it onto a
dark-colored table. Fill a pitcher. Fill a garbage can. What will you
do with a garbage-can full of "nothing?"
Fill a bowl with extremely dense mist (use a smaller hole in the aluminum
foil.) Let everyone slowly place their hands in it. It looks like milk,
but feels like nothing.
Fill an empty aquarium with mist. Place a square of cardboard vertically
in the aquarium, scrape it sideways, then lift it vertically. The pool of
mist will show surface waves, it will slosh back and forth. Stick your
hand in the pool and make it slosh.
Make a smoke-ring launcher from a coffee can and a balloon: Use a can
opener to remove both ends from the can. Cut the balloon open, stretch it
across the open end of the can, and secure it with tape. Place the
plastic coffee-can lid on the other end of the can. Cut a hole (2cm to
start) in the lid. If you gently tap or pluck the rubber membrane, the can
will launch a transparent ring-vortex through the air. Shoot these
invisible smoke rings into a pool of fog. Or fill the can with mist and
launch visible smoke rings!
Build a crude model of a small town, then let the fog roll in!
Fill an empty aquarium with mist. Place a clear lightbulb a few feet
away, then play with lenses above and within the mist. The focussing
effect of convex lenses is totally obvious. Take your fog-quarium out
into the sun and see how a magnifying glass can focus light. Obtain a
pair of colored light bulbs, red and green, and place them near each other
a couple of feet away from the mist. A convex lens will then clearly
display all the geometry of real-image formation and camera operation!
Try this with a string of christmas lights instead of the two lightbulbs.
Try it with a laser...
Place a large, lightweight cup or bag upon a beam-balance and weigh it.
Fill it with mist. What is the weight per unit volume? How big would a
pound of humidifier mist be?
A hint for visualizing our world: air is not invisible, it is transparent,
and air to us is like water to a fish: we can't see it, so we think it's
not there. If a plume of dirty water invades a pool of clear water, a
fish might see the dirt the same way that we humans think of smoke. To a
fish, dirty water looks like "smoke". We who live outside the water know
that the fish is really just seeing dirty water mixing in with the clean.
Without the water, the dirt wouldn't act like underwater smoke, it would
fall to the bottom. So, what is humidifier mist? It's not just water
droplets, since water droplets alone would instantly fall like rain.
Actually, humidifier mist is "dirty" air. It is air that's been stained
white with some other substance. Humidifer mist makes air visible. Adding
mist to the air is like adding dirt to the water. If the fish's world was
without water, the dirt would not float and couldn't look like smoke. If
we lived in an airless vacuum, the mist droplets would fall like so much
sand. Smoke and fog cannot exist in vacuum, because smoke and fog really
are air which is stained. Fires in a vacuum would not smoke, instead they
would shoot out fine grey powder at high speed.
(1)Clouds are water droplets, and water is heavy. Why do clouds stay
up, yet mist from the humidifier falls downwards? There are
several reasons.
Evaporated water is a gas like any other. Will it rise like Helium, or
fall like Carbon Dioxide? Here are some molecular weights:
GAS WEIGHT
H2 2
He 4
H2O 18
N2 24
O2 32
CO2 44
So, water-gas or "evaporated water" is lots heavier than hydrogen or
helium gas. Yet it's lighter than air, it is lighter than Nitrogen or
Oxygen. So, air that contains evaporated water will rise. Cumulus
clouds, the white puffy clouds seen in fair weather, are created by rising
plumes of humid air, and the bouyant water vapor helps keep the small
water droplets suspended. The humid air always goes upwards like helium.
When humid air becomes filled with water droplets, it turns white, yet
still goes upwards.
A second and more important reason: when air rises in the open atmosphere,
it moves into a region of lower pressure, expands, and the air temperature
drops. If the rising air is full of evaporated water, the water can
condense and become white mist made of tiny droplets. When condensation
takes place, energy is released, SO THE AIR BECOME WARMER. (Remember, it
takes energy to boil water, it also takes energy to cause evaporation,
while during condensation the opposite occurs and energy is returned. As a
result of the energy release, rising air with condensing droplets stays
warmer than surrounding air, so it expands more than it should, and it
ends up becoming less dense than the surrounding air. This drives the air
upwards. In other words, "hot air rises." Clouds are warm, and they
remain aloft for the same reason that hot air balloons do. If you could
heat up the humidifier mist enough, it would rise too.
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William Beaty voice:206-762-3818 bbs:206-789-0775 cserv:71241,3623
EE/Programmer/Science exhibit designer http://amasci.com/
Seattle, WA 98117 billbeskimo.com SCIENCE HOBBYIST web page