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 OBJECTIVES:
ONLINE READER: Atmospheric pressure refers
to the weight of the air exerting a force or pressure on an object.
All things, living and non-living, are subjected to this pressure.
Students do not usually think of themselves as being on the surface of the
Earth with tons and tons of air on them. They assume that they could
not possibly be able to walk around with such pressures placed upon them. An instrument called a
barometer measures the atmospheric pressure. An analog to a barometer is a Air has weight and hence creates pressure. The weight pulls down on us and creates a pressure. The pressure is equal in all directions. In this activity the students will use different bubble makers to discover that the reason bubbles are spheres, is because the pressure acts on their surface equally, forming a sphere. In space where is there is not air pressure, the pressure is still equal so you will still get spherical bubbles. PROCEDURE:
Today we talk about air pressure.
first you will watch a video and then we do 4 experiments.
1.
watch the video
Atmospheric pressure:
https://www.youtube.com/watch?v=xJHJsA7bYGc
(5 min)
2. Activity 1.
Demonstrate the card with the water (as was shown in the video).
Have them tell you why the water doesn't fall.
(Air pressure from below is stronger than gravity acting on the
water.) Let the students repeat at
their tables. Be sure to have
a tray or bucket under them for when the water comes out.
3.
Activity 2.
handboiler: An
instrument called a barometer measures the atmospheric pressure. An analog
to a barometer is a handboiler or love meter. Let one of the
students hold the meter in their hand. The class should observe what
happens and try to figure out what causes the liquid to boil.
The liquid inside a hand boiler does not actually boil. The "boiling" is
caused by the relationship between the temperature and pressure of
a gas. As the temperature of a gas in a closed container rises, the
pressure also rises. There must be a temperature (and pressure) difference
between the two large chambers for the liquid to move. When held upright
(with the smaller bulb on top), the liquid will move from the bulb with
the higher pressure to the bulb with lower pressure. As the gas continues
to expand, the gas will then bubble through the liquid, making it appear
to boil. The fact that the liquid is volatile (easily vaporized) makes the
hand boiler more effective. Adding heat to the liquid produces more gas,
also increasing pressure in the closed container.
IMPORTANT! students should be
warned that the boiler is made of thin glass and can break easily.
If it breaks they should let you know immediately but if they are
careful there should be no problem.
The liquid inside is not toxic, but the glass is dangerous.
Activity No. 3: Making a
helicopter
Can air be captured to help machines fly? Yes, take for instance the
helicopter out of paper. Make the helicopter using the instructions.
You will just need scissors and a paper clip (and crayons if they
want to decorate). They drop
(or throw) the helicopter and the air supports the "blades" and makes the
helicopter spin and float.
Ask them, if the helicopter would fly on the moon?
(No because there is no air pressure there—it would just drop).
They should put their name on the helicopter and get to take it home.
Activity No. 4: Making soap
bubble makers with wire.
Air has weight and hence creates pressure. The weight pulls down on
us and creates a pressure.
The pressure is equal in
all directions. In this activity the students will use
different shaped bubble makers to discover that the reason bubbles are
spheres is because the pressure acts on their surface equally, forming a
sphere.
Prepare bubble solution a few days before lab (see end for recipe)
1. Students should form the wire into various non-round shapes (square,
rectangle, triangle etc) and before using it predict if the bubble
will be shaped like their form or be round.
They should dip them in the solution and see if the bubbles are the
same shape as the form or they are round.
Have them try a variety of different shapes and see if there are
any differences.
Why do bubbles stay round?
(the air pressure is affecting them equally on all sides making them
round.) Why don't the bubbles
just contract due to the air pressure on the outside?
(There is air pressure on the inside pushing out in all
directions).
Students do not get to take the wire.
It can be reused for the next class.
At the end of the class have them students straighten the wire
before they leave.
summary questions:
1.
What is air pressure?
(pressure from gravity acting on air molecules).
2.
If air pressure is so heavy, why doesn't it crush a table (or us!)
(Because pressure is equalized above and below a table, inside and
outside us, etc.
3.
What causes air movement (wind)?
Differences in air pressure such as in a balloon or caused by heat
such as in the hand boiler
BUBBLE SOLUTION RECIPES
Make bubble solution ahead of time as it works better if it has set for at
least a couple of days.
A solution of dawn and water works well though there are a variety of
recipes on the internet. It
is often recommended to add a bit of glycerin though we have had success
with just Dawn and water.
Basic recipe is approximately 6 cups of water to 1 cup of Dawn plus 1
tablespoon glycerin. Add a
bit more Dawn if you are not getting the bubbles.
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handboiler or love meter. Let one of the students hold the meter in
their hand. The class should observe what happens and try to figure
out what causes the liquid to boil. Many will assume that the heat
of the hand boils the liquid, but it doesn't. The liquid
inside the glass chamber is usually methyl alcohol or another liquid that
has a low vaporization rate. The heat of the hand starts to vaporize
the liquid, that in turn changes the pressure inside the chamber and
forces the liquid up. The air in the chamber then is forced up after
the liquid is up and it appears like it is boiling.