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BALLOON IN A BOTTLE
Predict: Which balloon will inflate faster?
Put an un-inflated balloon inside a bottle. Fold the opening of the balloon
back over the mouth of the bottle so that it stays in place. Apply your lips
to the bottle and try to inflate the balloon. Do this as a race with one
balloon inside the bottle and another outside the bottle.
Explain: Why was the balloon in the bottle harder to inflate?
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[Note: For health reasons you will need one balloon for each student who tries to do the
demonstration.]
COLLAPSING CAN
Predict: What will happen when the heated can is cooled suddenly?
Place 5 rnL of water in the bottom of an empty aluminum soft drink can.
Heat the can on a hot plate until you see steam corning out of the opening.
Use tongs to quickly invert the can into a dishpan filled halfway with cold
water. The can will collapse suddenly and dramatically.
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C;
Explain: What causes the can to collapse?
SUBMERGED
CUP
Predict: Will the paper get wet?
Fill a large beaker about 2/3 full with water. Crumple a dry piece of paper
and squeeze it to the bottom of the plastic cup. Invert the cup making sure
that the paper stays up in the cup and immerse it completely under water
holding it as vertically as possible. Take the cup back out of the water and
put it on a paper towel to let the water drip off. Take the crumpled paper
out of the cup to show that it remained dry.
®
Q
Explain: Why didn't the paper in the cup get wet?
HOSEWITHWATER
Predict: How is it possible to change the water levels?
Hold a three-foot piece of clear plastic tubing in a U'-shape with the open
ends pointing up. Fill the tube about half full of water. Place a syringe
with the barrel pushed down halfway on one side of the tube. Make sure
the seal to the syringe is airtight. Push the barrel of the syringe in. Observe
what happens to the water levels on both sides of the tube. Pull the barrel
of the syringe out. Observe what happens to the water levels.
Explain: Why do the water levels change on either side of the tube as the
barrel of the syringe is pushed in and pulled out?
Lesson 1 - Balancing Act
Investigation III - Moving Matter
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@CUPANDCARD
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Predict: What will happen when the cup, water, and card are turned upside
down?
Fill a clear plastic cup partially with water. Place a card over the top of the
cup. Cardboard will work, but waterproof poster board or laminated
cardstock is preferable. Hold the card to the mouth of the cup and invert.
You can now let go of the card: it remains suspended and the water does
not spill out.
(j)
~
Explain: Why doesn't the card fall?
EXPANDING BALLOON (Version 1 - with a vacuum pump)
Predict: What will happen to the balloon?
Inflate a balloon to about 2 or 3 inches in diameter. Place the balloon
inside a flask that can be evacuated such as a side arm flask or a
dessicator. Seal the container (e.g., put a stopper on the flask) and connect
it to a vacuum pump. Turn on the vacuum pump to increase the size of the
balloon. Then allow the air back in to decrease the size of the balloon.
&
((;)
Explain: Why does the balloon increase in size in the vacuu.m chamber?
EXPANDING BALLOON (Version 2 - without a vacuum pump)
Predict: What will happen to the balloon?
Obtain a flask with a two-holed rubber stopper that
fits into the mouth of the flask. Put a piece of glass
tubing through the two holes in the stopper. Attach a
balloon or plastic bag to the bottom of one of the
pieces of glass tubing so that there is an airtight seal.
Put the stopper on the flask so that the balloon is on
the inside. If you "suck" on the glass tubing that
does not have the balloon attached to it, the balloon
will inflate slightly inside the flask. You can also use
an aspirator to remove air from the flask.
Explain: Why does the balloon increase in size in the
vacuum chamber?
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Weather© DC Regents, LHS Living by Chemistry, 2003.
rr-
Investigation III - Moving Matter
Lesson 1 - Balancing Acr
(~MARSHMALLOWS
V
(Version 1 - with a vacuum pump)
Predict: What will happen to the marshmallows?
Place several marshmallows inside a flask that can be evacuated such as a
side arm flask or a desiccator. Seal the container (e.g., put a stopper on the
flask or the dome lid on the desiccator) and connect it to a vacuum pump.
Turn on the vacuum pump to increase the size of the marshmallows. Then
allow the air back in to decrease their size. They will be smaller than they
were when you started.
.
Explain: Why does the marshmallow increase in size inside the vacuum
chamber? Why is the final size of the marshmallow (after the air is
returned to the vacuum chamber) smaller than the original size?
(VMARSHMALLOWS (Version 2 - without a vacuum pump)
Predict: What will happen to the marshmallows?
-"--'"
Put a marshmallow inside a plastic syringe. Move the plunger down close
to the marshmallow with the opposite end open to allow air to escape. Do
not crush the marshmallow. Seal the tip of the syringe and pull back on the
plunger. The marshmallow grows bigger. Then, push the plunger back in.
The marshmallow grows smaller.
Explain: Why does the marshmallow increase in size when you pull back
on the plunger of the syringe?
Making Sense Discussion
(15 min)
Major Goals: Most of this discussion may actually take place as each demonstration
is conducted. Students should be allowed to share what they observed and what they
think happened in each case. It is important to focus on how air pressure changed in
each demo and, then, how each system ultimately stabilized the air pressure. Air
pressure should be defined and air pressure as it relates to weather should be briefly
touched on.
S. Discuss what happened in each demonstration.
Ask groups of students to put their drawings on the board with arrows
showing air pressures. Some sample drawings are included below. Ask
students to consider air pressure inside and outside of each container.
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/
Balloon in a flask demo
Crushed can demo
Lesson 1- Balancing Act
Investigation III - Moving Matter
Int,
Tn
n
1
Paper in cup demo
Hose with water demo
Discussion goals:
Assist the class in sharing explanations of what happened for each
demonstration.
Sample questions:
Why is it so difficult to inflate the balloon inside the flask?
What causes the can to collapse?
Why does the paper stay dry?
Why do the water levels change on either side of the U-tube as the barrel of
the syringe is pushed in and pulled out?
Why doesn't the card fall?
Why does the balloon increase in size in the vacuum chamber?
Why does the marshmallow increase in size inside the vacuum chamber?
Why is the [mal size of the marshmallow (after the air is returned to the
vacuum chamber) smaller than the original size?
Points to cover:
In each demonstration air is trapped somewhere. In each demonstration the
pressure of the trapped air is changed or the pressure of the air on the outside
of the container with the trapped air is changed.
Balloon in a Bottle: In the first demo we tried to inflate a balloon inside a
flask. The flask already has air in it from the surrounding atmosphere. When
we try to put air into the balloon we meet with the pressure from the air
already in the container on the outside of the balloon. The air pressure inside
the balloon and outside the balloon push against each other. Ultimately the air
pressure inside and outside of the balloon will be equal.
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Collapsing Can: In the second demonstration, water inside a soda can is
heated to boiling and fills the can with water vapor. Some of this water vapor
can be seen escaping from the can in the form of steam. When the can is
placed upside down in cold water the water vapor is turned quickly into liquid
Weather© UC Regents, LHS Living by Chemistry, 2003.
157
Investigation III - Moving Matter
Lesson 1 - Balancing Act
water. The result is a dramatic decrease in air pressure inside the can. The can
collapses quickly as the air pressure inside and outside the can stabilize and
become equal.
@
Submerged Cup: In this demo some paper is squished into the bottom of a
cup. Now there is air and paper in the cup. When the cup is inverted in some
water, the air trapped inside the cup is squeezed into a smaller space and
exerts a pressure on the water. As a result the water only goes part of the way
up the inside of the cup. The paper stays dry.
Hose with "Vater: In this demonstration one end of a hose is sealed off with
a syringe. The space available for that trapped air can be made smaller or
larger by moving the plunger on the syringe. The water in the hose can be
seen to move as a result of the increase or decrease in air pressure at one end.
The air pressure of the trapped air is always in balance with the air pressure
outside the hose because the water inside the hose is able to move. The
unequal water levels are a direct measure of difference in air pressure trapped
in the syringe and in the atmosphere.
@
(f)
'@
Cup and Card: A cup with water and air inside is inverted with a card
covering the mouth of the cup. This causes the card to be suspended, and the
water does not spill out of the cup. The air pressure pushing up on the card
from the atmosphere is larger than the weight of the water and the card. [Note:
If you observe carefully, you will notice that a small amount of water spills
out when you invert the cup. This decreases the volume of water inside the
cup and increases the volume occupied by the air on the inside. The result is
that the air pressure on the inside is less than the air pressure on the outside.]
Expanding Balloon: A slightly inflated balloon is placed inside a vacuum
chamber and the air outside the balloon is pumped out. The balloon increases
in size. The pressure from the air outside the balloon is decreasing as the air is
pumped out of the chamber. Thus the balloon increases in size until the air
pressure outside the balloon and the air pressure inside the balloon are equal.
Chubby Marshmallows: Marshmallows have tiny pockets of trapped air
within them. When the air outside the marshmallows is removed, the air inside
the marshmallows expands and the marshmallows puff up. The air pressure in
the pockets inside the marshmallows is equalizing with the air pressure
outside the marshmallows. Some of the air pockets within the marshmallows
will burst, so when air is put back in the chamber the marshmallows may
actually be smaller than they were before.
In all the demonstrations, air was trapped in a container in which the volume
could vary. These "stretchy" containers included balloons, water, and sugar
pockets inside the marshmallow. In each demonstration, the air pressure is
changed by changing some part of the system (air is added to a balloon. air is
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heated and then cooled quickly, air is squeezed in a syringe, etc.) Because of
the stretchiness of the containers, each system was able to stabilize until the
air pressure outside and inside the containers was equal.
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