Download PRESSURE STATION 4

STATION 1
Balloon in a Vacuum
***CAUTION***: at this station, all students must wear eye protection the entire time the vacuum
pump is in operation. Please be careful and use the equipment as directed. Failure to follow
directions could lead to serious injury or death. Thank you for following directions.
PURPOSE: To show the affect the atmosphere has on objects on this planet.
Questions:
1. What did the balloon do when you turned on the vacuum pump? Why?
a. Expand because the air pressure decreased inside the glass container
and allowed the air in the balloon to increase in volume.
2. Why don’t we feel or really notice the atmosphere?
a. Because it pushes equally on us from all sides. It is also because we
are mainly water and water does not compress when pressure
increases.
3. What does the balloon look like when the air pressure goes back to normal?
Where in the real world could a vacuum be used for consumer goods or in
the real world?
a. It looks like normal before you stated the vacuum pump.
b. Vacuum-packed foods (the stuff the astronauts eat or the pop you here
when you open up a bottle of Snapple’s. The safety feature to let you
know that no one opened the bottle before you purchased it).
4. Explain what happens to a bag of potato chips when you go up in an
airplane? What would the bag look like after you landed if, during the
flight, you opened the bag then sealed it while at 30,000 feet? Why?
a. When the bag goes up in elevation there is less atmospheric pressure
(because there is less air as we go up). This allows the air inside the
bag to expand and increase the volume of the bag (so it gets big and
puffy).
b. If you opened (and closed again) it at 30,000 feet where the
atmospheric pressure is less than sea level, the bag would be
compressed when the plane lands because the atmospheric pressure is
greater at sea level. The chips would still be a tasty treat that could
still be enjoyed as the cornerstone of any nutritional meal (what movie
is that inspired from?).
STATION 2
Three Holes and a Bottle
PURPOSE: To show what causes air pressure & that it does not discriminate.
Questions:
1. Which hole has a stream that goes the furthest? Explain what is causing
what you are seeing to happen?
a. The bottom stream goes the furthest because it has the greatest amount
of pressure on it. It happens because it has the most water plus the
atmosphere applied to it. The atmosphere, plus the water above each
hole is what is applying the pressure for the water to squirt out the
holes.
2. What is forcing the water to move out of the holes? What force is keeping
all the level of the red liquid the same in four glass tubes?
a. Air pressure and the weight of the water above it.
b. Air pressure (atmospheric pressure).
3. What force is causing the atmosphere to push down on us?
a. Gravity is what is causing there to be air pressure. If there was no
gravity, there would not be a force forcing down the air.
4. If you were on Mars where the atmosphere is 1/100th as thick as our
atmosphere, would the water shoot out further than on Earth?
a. No, the water would not shoot as far for two reasons. First, the
gravity on mars is less than on Earth (2/3rd). This means there is less
force pulling the atmosphere towards the ground (so less air pressure).
Second, the atmosphere is 1/100th as thick so there is less mass
pushing down on the planet. The decrease in pressure results in a
decrease atmospheric pressure.
5. Why do we feel a lot of pressure on our ears when we swim to the bottom
of a pool (12 feet or 4 meters deep), but do not feel the same pressure when
we go down a flight of stairs (12 feet or 4 meters down)?
a. This is due to the pressure applied by the water on your Eustachian
tubes (the ones that pop when you go up in an airplane or the
mountains). Since water has a density of 1 g/cm3 and air has a density
of .0012g/cm3 (or almost 1000 times less dense), there is more mass
(and pressure (force)) pushing on your body.
b. FYI – the atmosphere has a pressure of 14.7 lb/in2. 32 feet of ocean
water is equal to one atmosphere. The atmosphere is approximately
20 miles high. It is the density of water compared to the density of air
that makes the difference in the pressure our body feels when we go
swim with Flipper in the beautiful ocean.
STATION 3
Under Pressure
*Pascal’s Principle- when force is applied to a fluid in a closed container the
pressure is transmitted equally to all parts of the fluid (gas / liquid).
Questions:
1. Which syringe is easier to push down? Explain it in terms of Pascal’s
principle.
The syringe with less surface area (the small syringe) is easier to push down. If
you look at the formula for pressure (P=Force/Area) you will see that force that is
needed to push down each syringe is different because the area (surface area) for
each syringe is different. Now, Pascal’s Principle states that the pressure in a
closed container is equally everywhere in the closed container. This means the
pressure on the water is the same in the big syringe as in the little syringe when
you push down on either one. If P (pressure) is equally on the liquid from each
syringe that means the force to move them will be different because the area each
one covers is different. The bigger syringe has a larger area so it will need to
have a bigger force applied to it compared to the small one.
2. Other than one syringe being harder to push then the other, what other
difference do you notice when you push down the larger vs. smaller
syringe?
The smaller one is easier to push down, BUT does not cause the big syringe to
move up as far as when the big syringe is pushed. The big syringe is moving a
larger volume of air so it causes the little syringe to move upwards more when
the big syringe is pushed.
3. Where is the pressure the greatest when you are pushing down on the small
syringe? Where is it the greatest when pushing on the large syringe?
The pressure is equal everywhere when pushing either of the syringes. This is
what Pascal’s Principle states.
4. Which syringe contains water with the greater density? Why?
The densities of the water are the same for each one for two reasons.
First, density of matter is unique to the matter. All water at STP
(standard temperature and pressure) has a density of 1 g/cm3. It does not
matter where the water is in the syringe it still is water.
Second, the water in the syringes is in a closed system with a force
being applied. According to Pascal the pressure on the water is equal
everywhere in the closed container. This means that the density (which
does increase slightly because of the increased pressure) is the same for all
the water in the syringes.
5. Which syringe can hold the greatest volume of water?
The larger syringe can hold the greatest volume of water and also the
greatest mass of water compared to the smaller syringe. The large syringe
can hold 60 ml (60 cc) of water and the smaller one can only hold 10 ml (10
cc).
6. Give three examples in the real world where you would see a hydraulic
(liquid filled) or pneumatic (gas filled) device that uses Pascal’s principle?
Three or more examples from the real world would be: bike pump, elevator,
hydraulic lift or press, shocks on a car, pogo stick, squirt gun, water pipes at
your home, thermometer, scuba tank, air compressor, air powered tools, air
bag in your car, and so many, many more…
STATION 4
Tornado in a Bottle
PURPOSE: To demonstrate how cyclones (low pressure systems) move and
how the physics we have studied are involved.
Questions:
1. Why do you need to swirl the bottle around? Will it work if you do not
swirl it around?
a. To get the potential energy to transfer to kinetic energy. If you do not
swirl the water around, the air pressure in the bottom bottle pushes on
the water above and does not allow it to go down. (It is like when you
put your finger on a straw filled with soda and the liquid does not fall
from the straw until you remove you finger).
b. Not really. You need to create low pressure in the middle so it will
start to flow. It has a low pressure middle because moving air has a
lower pressure than still air. Remember, warm air rises and cold air
sinks. In the eye of the storm, there is cold, dry air descending.
2. Which way do storms (low pressure systems) rotate in the Northern
hemisphere? Which way do high pressure (anticyclone) systems rotate?
What happens in the Southern hemisphere?
a. In the Northern hemisphere, low pressure (cyclones) rotate
counterclockwise. High pressure (anticyclones) rotate clockwise. In
the Southern hemisphere, low pressure systems rotate clockwise and
high pressure rotate counterclockwise.
3. What principle of physics explains why the middle should have no water in
it (think roller coaster project)? What is the middle a hurricane called?
a. The force that goes towards the outside of a circle, the centrifugal
force (also Newton’s First Law of Motion – things in motion tend to
stay in motion). Water swirls the fastest at the outer part of the
tornado and slower in the middle (just like the propeller of a plane or a
merry-go-round. It is the most fun to be on the outside of this type of
ride because it spins faster compared to the middle).
b. The eye. Cold, dry air descends in the middle of the eye. It is low
pressure and generally the calm part of the storm. People enter the
eye and get a false impression that the hurricane is over. There is still
the other side of the hurricane to come.
4. When and where (in the United States) do tornados usually form? What
types of fronts or conditions are involved?
a. During the spring, time in the Midwest.
b. When warm, moist air from the Gulf of Mexico meets with cold, dry
air mass from the North. Cold fronts from Canada meeting warm
fronts from the Gulf of Mexico.
5. How are hurricanes and tornados similar? How do they differ?
a. Both have violent winds and can cause serve damage and destruction.
Both have a low pressure middle (the eye) where the winds are calm
(the eye in the tornado is very small so there really isn’t a calm in a
tornado). Cold dense air descends (goes down) and warmer moist air
ascends (goes up). Hurricanes occur over warm ocean waters and
tornados form over land where warm & cold fronts meet.
STATION 5
Moving Air while Moving Bodies
PURPOSE: To show the relationship between pressure and volume. To show that moving air
is less dense than stagnant (still air) and that cool, unexpected things happen because of this
(Bernoulli’s Principle). IMPORTANT: moving air is less dense than still air.
Questions:
Part I:
“Rolling Coke Cans “
1. Which way does the coke cans roll?
a. To the middle. This is where the volume of air has increased (more
space between air molecules, less dense (density = mass/volume), but
the pressure is less so the cans want to go where there is less pressure
or push on them. This is why motorcycles are pulled towards on
coming big rigs on two lane highways. Bernoulli’s Principle states
that the faster the air moves, the less pressure it exerts.
2. Where is the air the densest? The least dense?
a. On the sides of the cans. In the middle where the air is moving.
3. When you blow through the cans, are you increasing or decreasing the
pressure? What about the density of the moving air?
a. Decreasing the pressure when you blow. The density is decreasing,
but the volume is increasing (air molecules are further apart, moving
faster). Bernoulli’s Principle (see vocab)
Part II: “Dancing Ping Pong Balls“
1. What happens to the ping pong balls when you blow between them?
a. They move closer together because of the low pressure you are
creating.
2. What happens if you blow on the outside?
a. The one you blow next to moves a little to the side. The tape on the
ping pong balls seems to have made it difficult for you to see that.
3. Explain what is happening?
a. There is lower pressure (less of a push by the air) so the balls move to
the lower pressure area (the middle) because the denser air is pushing
it towards the less dense air. The density has decreased so now there
is more room for air and the ping pong balls to slide into.
STATION 6
Pressure & the Cartesian Divers
PURPOSE: To show how gases and liquids react to increased pressure and how the changing
of air’s density causes the Cartesian diver to move.
Part I: Squidy, Hook, Spinner, & Friends
Questions:
1. Why does Squidy, Hook, or Spinner go to the bottom of the bottle when
you squeeze it (talk about the density of the air, not the water)?
a. The pressure is increasing on the air, so the density of the air inside the dropper
increases. When the dropper is first put into the bottle it just barley floats because
its density is just a tiny bit less than the water. When you squeeze the bottle, you
are increasing the density of the water and the air inside the little diver person.
Right now you are probably saying, “Well, Mr. Mathot, if the density of the water
is now greater, shouldn’t the diver person float better?
That is a very good question, very good, even logical. BUT: The air in the diver
person is also increasing in density. In fact, the density of the air is changing more
than that of the water. Here is the KEY: Air is easier to compress and make denser
compared to water (water doesn’t compress very well). When you squeeze the
bottle, the air in the diver person is compressed (decreases in volume) so much that
it changes the density (density=Mass/Volume) enough for the diver person to now
be denser than the water and sink to the bottom.
Part II: Air in a Syringe
Questions:
1. What does the syringe filled with air remind you of in the real world? How
could it be used or where is it used in the real world?
a. It might remind you of a air pump, needle at the doctor’s office, a piston
on a machine, shocks on a bike, or anything else that is a closed
container filled with a fluid (gas or liquid).
2. Which syringe is easiest to compress (water filled or gas filled)? Explain why
using density and your knowledge of liquids and gases.
a. The gas (air filled) syringes. This is because air is less dense than water.
Air still has space for the molecules to be pushed together. Water is too
dense for it to be compressed further (for the most part). Let me give
you an example: Someone in 1st or 2nd period was so strong (or they did
not follow Mr. Mathot’s warning) they cracked the plastic of the water
filled syringe. The water did not want to be compressed anymore so the
force was transferred into the plastic and cracked it.
3. Could you ever compress the syringe completely if it was full of air? Explain
your answer.
a. No, because the air takes up space and needs space to exist in (you can
not destroy matter). The pressure would increase so much that either the
container would explode or there could not be any more pressure applied
to the air in the container.
Gas Laws – VTP Lab
V
Volume
T
Temperature
P
Pressure
Conclusion/Questions:
Part A
1. Put your pencil through the middle hole (that is holding the temperature constant);
push down on the part of the card labeled volume. That shows the effect of lowering
the volume. What happens to the volume when the pressure is increased?
a. The volume decreases.
2. What happens to the volume when the pressure is decreased?
a. The volume increases.
3. What GAS LAW states this?
a. This is Boyle’s Law.
Part B
4. Place a pencil through the pressure hole indicating holding pressure constant. What
happens to the volume if you decrease the temperature?
a. The volume decreases.
5. What happens to the volume if you raise the temperature?
a. The volume increases.
6. What GAS LAW states this?
a. This is Charles’s Law.
Part C
7. Place a pencil through the volume hole. This indicates holding volume constant. What
happens to the pressure if you raise the temperature?
a. The pressure increases.
8. What happens to the pressure if you lower the temperature?
a. The pressure decreases.
9. Why do you think gases can be compressed, but liquids and solids cannot?
a. Gases can be compressed because they are less dense than liquids and solids.
Liquids and solids cannot be compressed much if at all because their atoms are
already very closely packed together (dense).
10.Why is it extremely dangerous to put dry ice in a closed container? Use your VTP
card to explain this puzzle.
a. The volume remains the same (until it explodes) while the temperature increases
(CO2 sublimes) and the causes the pressure to increase greatly.
BONUS: If you increase the pressure then you increase the density because the
molecules are “squeezed” closer together (denser).
CARTESIAN DIVER Lab
(A LOOK AT Pascal’s Principle)
Answers
1. See the three purposes from the lab sheet.
2. The dropper goes down to the bottom when you squeeze the bottle and it
goes back up to the top when you release. If you look at the diver when
you squeeze the bottle you will notice that the air gets compressed and the
volume of the air decreases. This causes the diver to increase in density and
sink. The opposite happens when you release the hounds from the bottle.
3. The pressure of the water increases and so does the pressure on the air.
The density of the air, however, changes more than that of the water. This
causes the diver to become denser than the water, even though, the diver has
air in it.
4. Some of the water is pushed into the dropper because air can be compressed
more than water because air is less dense and liquids in general do not
compress much when there is a force applied.
5. The diver sinks because the force (of pushing on the bottle) causes the water
to have more pressure on it and that results in the air having more pressure
on it. The density of the water stays almost the same, but the density of the
air increases so that now the Cartesian diver dude is denser than the
water. This is why he/she goes to the bottom (it’s all about density).
6. If the density of an object is less than the fluid, it will FLOAT. If the
density is greater than the fluid, it will SINK. Water has a density of 1
g/cm3 (fresh). This means if the density of a piece of wood is .8 g/cm3 the
wood will float.
7. When pressure drops the density of air decreases (becomes less dense and
more spread out (larger volume)).
8. When pressure increases the density of air increases (becomes denser and
less spread out (smaller volume)).
9. It is equal in pressure everywhere in the fluid. Pressure, like gravity, does
not discriminate.
10. Gases are less dense than liquids and solids and still have room for their
atoms to get denser.