Demos / DiscussionDemos / Discussion

• Crush can demoCrush can demo

• What crushes the cans? What crushes the cans?

• Marshmallow demoMarshmallow demo

• Why does the marshmallow blow up in Why does the marshmallow blow up in a vacuum? a vacuum?

• Why does the bell jar stick to the base?Why does the bell jar stick to the base?

• Glass of water demo Glass of water demo

• Why does the water stay in the glass?Why does the water stay in the glass?

Lesson #49Lesson #49Topic: Atmospheric PressureTopic: Atmospheric Pressure

Objectives: Objectives: (After this class I will be able to)(After this class I will be able to)

1.1. Describe Atmospheric Pressure.Describe Atmospheric Pressure.

2.2. Describe Bernoulli’s Principle. Describe Bernoulli’s Principle.

1/22/07

Assignment: Book Problems Ch 20 Review Questions #8, 10, 12, 17 Think and Explain #5

Warm Up: The air pressure in this room is 100000Pa. The area of the palm of your hand is approximately 180cm2. What is the force exerted onto you hand by air? Why don’t you feel this force on the palm of your hand?

Atmospheric PressureAtmospheric Pressure• The weight of the earth’s atmosphere The weight of the earth’s atmosphere

exerts pressure onto all things on the exerts pressure onto all things on the earth.earth.

• Air presses onto all parts of our body. Air presses onto all parts of our body.

• Because it presses equally everywhere, Because it presses equally everywhere, we do not notice this pressure. we do not notice this pressure.

• However, if we were to remove this However, if we were to remove this constant pressure, we would not survive.constant pressure, we would not survive.

• We live on the bottom of an ocean of air.We live on the bottom of an ocean of air.

Fluid PressureFluid Pressure

• Air can be treated as a fluid just like Air can be treated as a fluid just like water.water.

• All fluids want to move from areas of All fluids want to move from areas of high pressure to areas of low high pressure to areas of low pressure.pressure.

• Demos:Demos:

• Balloon/Flask demoBalloon/Flask demo

• Why does the balloon blow up?Why does the balloon blow up?

• Where does wind come from?Where does wind come from?

Demos / DiscussionDemos / Discussion• Ping pong and straw.Ping pong and straw.

• How is the ball floating?How is the ball floating?

• Ping pong in sink.Ping pong in sink.

• Why does the ball stick to the water?Why does the ball stick to the water?

• Ball and blower.Ball and blower.

• Why does the ball float?Why does the ball float?

• Cans on rollers.Cans on rollers.

• Why do the cans go together?Why do the cans go together?

• Why are piers for ships built so that water Why are piers for ships built so that water can pass underneath? can pass underneath?

Bernoulli's Principle Bernoulli's Principle • Moving fluid exerts less pressure than non-Moving fluid exerts less pressure than non-

moving or slower moving fluid.moving or slower moving fluid.

• Example: A bag getting “sucked” out of a Example: A bag getting “sucked” out of a car window.car window.

• The pressure of the moving air outside of The pressure of the moving air outside of the window is less than the pressure inside. the window is less than the pressure inside.

• Air (and the bag) then move from high Air (and the bag) then move from high pressure (inside) to lower pressure pressure (inside) to lower pressure (outside). (outside).

• What happens to the bag when it is sitting What happens to the bag when it is sitting along side of the road and another car goes along side of the road and another car goes by?by?

Bernoulli's Principle of FlightBernoulli's Principle of Flight• This concept of pressure was put to use This concept of pressure was put to use

by the Wright brothers.by the Wright brothers.• Notice the shape of the wing of an Notice the shape of the wing of an

aircraft.aircraft.

• The shape is designed to create less air The shape is designed to create less air pressure above the wing than below pressure above the wing than below the wing.the wing.

Bernoulli's Principle of FlightBernoulli's Principle of Flight• The air passing the top of the wing will travel a The air passing the top of the wing will travel a

greater distance in the same amount of time as greater distance in the same amount of time as the air passing the bottom of the wing.the air passing the bottom of the wing.

• This will create a difference in the velocity of the This will create a difference in the velocity of the air, and therefore a difference in pressure.air, and therefore a difference in pressure.

• This and Newton’s Third Law allows flight to This and Newton’s Third Law allows flight to occur.occur.

Slower Air

Faster Air

Wing

Bernoulli’s principle is, faster moving Bernoulli’s principle is, faster moving fluid will exert ______ pressure than/as fluid will exert ______ pressure than/as slower moving fluid.slower moving fluid.

More

Les

s

The

sam

e

I hav

e no id

ea

0% 0%0%0%

1.1. MoreMore

2.2. LessLess

3.3. The sameThe same

4.4. I have no ideaI have no idea

0of20

Lesson #50Lesson #50Topic: Lab: Atmospheric PressureTopic: Lab: Atmospheric Pressure

Objectives: Objectives: (After this class I will be able to)(After this class I will be able to)

1.1. Apply the concept of force per area to Apply the concept of force per area to calculate the air pressure in the room.calculate the air pressure in the room.

1/24/07

Lab Task: Use a syringe and known weight to calculate the atmospheric pressure of the classroom.

Warm Up: The air in a classroom exerts a force of 40N onto an area of 4cm2 what is the air pressure in the room?

Assignment: Lab report due tomorrow.

The air in a classroom exerts a force of 40N onto an area of 4cm2 what is the air pressure in the room?

10

Pa

160

Pa

0.1

6 Pa

100

,000

Pa

160

,000

Pa

0% 0% 0%0%0%

1.1. 10 Pa10 Pa

2.2. 160 Pa160 Pa

3.3. 0.16 Pa0.16 Pa

4.4. 100,000Pa100,000Pa

5.5. 160,000Pa160,000Pa

0 of 20

ProjectProject

• With your partner, write a paragraph With your partner, write a paragraph or draw a picture on a sheet of paper or draw a picture on a sheet of paper explaining how an airplane is capable explaining how an airplane is capable of flying.of flying.

• When finished, fold this sheet of When finished, fold this sheet of paper into an airplane and throw it to paper into an airplane and throw it to the front of the room.the front of the room.

Lesson #51Lesson #51Topic: Pascal’s Principle and Hydraulics Topic: Pascal’s Principle and Hydraulics

Objectives: Objectives: (After this class I will be able to)(After this class I will be able to)

1.1. Explain and describe Pascal’s Explain and describe Pascal’s Principle.Principle.

1/25/07

Assignment: Pascal’s Principle

Warm Up: Explain how Bernoulli's Principle with Newton’s third law allow flight to occur.

Pascal’s PrinciplePascal’s Principle• This is the simple idea that the pressure This is the simple idea that the pressure

exerted into a system must be the exerted into a system must be the pressure that you get out of a system.pressure that you get out of a system.

• Example:Example:

• PPinin=P=Poutout

• How is this useful?How is this useful?

PinPout

Pascal’s PrinciplePascal’s Principle• For the small section of tube, there is a small For the small section of tube, there is a small

amount of force exerted onto a small area.amount of force exerted onto a small area.

• Because the pressure has to remain the same, Because the pressure has to remain the same, if the area of the system gets larger, then the if the area of the system gets larger, then the force exerted must get larger as well.force exerted must get larger as well.

Fin Fout

out

out

in

in

A

F

A

F

Pascal’s PrinciplePascal’s Principle

• This is useful because we can now lift This is useful because we can now lift heavy objects with only exerting a small heavy objects with only exerting a small amount of force. amount of force.

• Example:Example:

• In the previous diagram 10N of force is In the previous diagram 10N of force is applied over a small area of 8cmapplied over a small area of 8cm22. This . This exerts pressure onto the opposite end of exerts pressure onto the opposite end of the system where the area expands to the system where the area expands to 1m1m22..

• What is the output force exerted by this What is the output force exerted by this end of the system?end of the system?

Lesson #52Lesson #52Topic: Exam 7 ReviewTopic: Exam 7 Review

1/26/07

Assignment: Exam 7 Review due ! Study for Exam 7.

Warm Up: A pump is used to inflate a tire. The initial tire pressure is 210kPa. At the end of the pumping process, the final pressure is 310kPa. If the diameter of the cylinder of the pump is 3cm, what is the average force exerted while pumping?

Objectives: Objectives: (After this class I will be able to)(After this class I will be able to)

1.1. Practice solving physics problemsPractice solving physics problems

2.2. Complete and check Exam 7 ReviewComplete and check Exam 7 Review

3.3. Plan a tutoring time (if needed)Plan a tutoring time (if needed)

4.4. Complete a bonus problem Complete a bonus problem opportunityopportunity

A pump is used to inflate a tire. The initial tire pressure is 210kPa. At the end of the pumping process, the final pressure is 310kPa. If the diameter of the cylinder of the pump is 3cm, what is the average force exerted while pumping?

367

.6N

148

.4N

219

.1N

183

.7N

0% 0%0%0%

1.1. 367.6N367.6N

2.2. 148.4N148.4N

3.3. 219.1N219.1N

4.4. 183.7N183.7N

0 of 20

Piers for ships are built on pillars so that Piers for ships are built on pillars so that water can pass underneath the pier so that water can pass underneath the pier so that ……

The

velo

city

of t

he wat

..

The

press

ure e

xerte

d ..

Both

1 &

2

Nei

ther

1 o

r 2

0% 0%0%0%

1.1. The velocity of the The velocity of the water on both sides water on both sides of the ship are of the ship are relatively the same.relatively the same.

2.2. The pressure exerted The pressure exerted on both sides of the on both sides of the ship are relatively ship are relatively the same.the same.

3.3. Both 1 & 2Both 1 & 2

4.4. Neither 1 or 2Neither 1 or 2

0 of 20

We don’t feel the force from the We don’t feel the force from the presence of air around us becausepresence of air around us because

The

forc

e is

too

weak

f..

All

the

forc

es d

ue to

a..

Our b

odies

do not r

ea..

None

of the

abo

ve

0% 0%0%0%

1.1. The force is too weak The force is too weak for us to feelfor us to feel

2.2. All the forces due to All the forces due to air on one side of our air on one side of our body cancel with the body cancel with the other side.other side.

3.3. Our bodies do not Our bodies do not react or push out react or push out against these forcesagainst these forces

4.4. None of the aboveNone of the above

0 of 20

A hydraulic lift works because of A hydraulic lift works because of Pascal’s principle that …Pascal’s principle that …

Forc

e in

to a

sys

tem

...

Pre

ssure

incr

ease

s t..

.

Pre

ssure

dec

reas

es ..

.

Pre

ssure

into

a s

yst..

0% 0%0%0%

1.1. Force into a system Force into a system equals force out of a equals force out of a systemsystem

2.2. Pressure increases Pressure increases throughout a systemthroughout a system

3.3. Pressure decreases Pressure decreases throughout a systemthroughout a system

4.4. Pressure into a Pressure into a system equals system equals pressure out of a pressure out of a systemsystem

0 of 20

Airplanes remain flying Airplanes remain flying through the airthrough the air

Eas

ier o

n th

e m

oon th..

Whe

n ther

e is

hig

h p...

Whe

n ther

e is

low p

r...

Whe

n the

air p

ress

ur...

0% 0%0%0%

1.1. Easier on the moon than Easier on the moon than on the earth because on the earth because gravity is less on the moongravity is less on the moon

2.2. When there is high When there is high pressure below and low pressure below and low pressure above the wingspressure above the wings

3.3. When there is low When there is low pressure below and high pressure below and high pressure above the wingspressure above the wings

4.4. When the air pressure When the air pressure above and below the above and below the wings are equal. wings are equal.

0 of 20

An empty plastic bottle is sealed so no air An empty plastic bottle is sealed so no air can escape. It is then taken up to the top of can escape. It is then taken up to the top of the earths atmosphere in a helium balloon. the earths atmosphere in a helium balloon. The bottle will …The bottle will …

Exp

and to

a m

uch la

r...

Cru

sh in

on it

self.

Do n

othin

g sin

ce th

e ...

Not e

nough in

fo to

say

0% 0%0%0%

1.1. Expand to a much Expand to a much larger size and larger size and possibly explode.possibly explode.

2.2. Crush in on itself.Crush in on itself.

3.3. Do nothing since Do nothing since the pressure inside the pressure inside and out are equal.and out are equal.

4.4. Not enough info to Not enough info to saysay

0 of 20

Approximately how much force Approximately how much force does the atmosphere exert on does the atmosphere exert on a piece of land that is 500m by a piece of land that is 500m by 400m?400m?

A 50kg girl sits on a 10kg chair A 50kg girl sits on a 10kg chair so that her body weight is so that her body weight is evenly distributed on the legs evenly distributed on the legs of the chair. Assume that each of the chair. Assume that each leg makes contact with the leg makes contact with the floor over a circular area with a floor over a circular area with a radius of 2cm. What is the radius of 2cm. What is the pressure exerted on the floor pressure exerted on the floor by each leg individually? by each leg individually?

• A hydraulic brake system is shown below. The A hydraulic brake system is shown below. The area of the piston in the master cylinder is area of the piston in the master cylinder is 8.4cm8.4cm22, and the area of the piston in the , and the area of the piston in the brake cylinder is 2.75cmbrake cylinder is 2.75cm22. The coefficient of . The coefficient of friction (friction (μμ) between the brake shoe and the ) between the brake shoe and the wheel drum is wheel drum is 0.50.5. Determine the . Determine the friction friction forceforce between the brake shoe and the wheel between the brake shoe and the wheel drum when a force of 55N is exerted on the drum when a force of 55N is exerted on the petal. petal.

Master Brake

BonusBonus• A paintball gun fires 2.5g paintballs A paintball gun fires 2.5g paintballs

1.5cm in diameter through the use of 1.5cm in diameter through the use of air pressure. If the pressure in the air pressure. If the pressure in the canister of compressed CO 2 in the canister of compressed CO 2 in the gun is 250000Pa, how fast is the gun is 250000Pa, how fast is the paintball moving when it reaches the paintball moving when it reaches the end of the 45cm long barrel? (2pts) end of the 45cm long barrel? (2pts)

• What is the maximum range of this What is the maximum range of this gun? (3pts) gun? (3pts)