Under Pressure
Mr. Sapone
Hypothesis:
Task: design and conduct an
experiment that tests your
hypothesis. You may use any
normal office supplies (balloons,
rulers, tape, string etc.) and any
lab equipment (rulers, balances,
beakers) you might need.
Conclusion:
Brief Procedure:
Data:
Bed of Nails: How does it work?
4
Forza Science!!!!!
Pressure = Force / Area
• Pressure is the amount of
force exerted over a given
area.
• P = F/A
– F is Force and the unit is
Newtons (N)
– A is Area and the unit is
Meters2 (m2)
– The unit for Pressure is N/ m2
or a Pascal (Pa)
– Force can also be measured
in pounds (lbs)
– Area can also be measured in
square inches
– Unis For Pressure can be psi
(lbs/in2)
• If force is constant but area
increases, pressure will
• If force is constant but area
decreases, pressure will
• If area is constant but Force
increases, pressure will
• If area is constant but Force
decreases, pressure will
6
A 100lb person laying on one nail
would result in a lot of pressure
at that one spot. (100lb/nail)
A 100lb person laying on two nails would
result in the pressure being spread out
more. 100lb/2nails = 50lb/nail
A person laying on 20 nails
displaces their weight over
all of them reducing the
pressure in each spot.
100lbs /20 nails = 5lbs/nail
Rank these from highest pressure to lowest pressure
1kg
2kg
Aluminum
1kg
3kg
Ice
1kg
1kg
Gold
1kg
4kg
Wood
[1]
[2]
[3]
[4]
[1]
[2]
[3]
[4]
[1]
[2]
[3]
[4]
f
p=
a
f
a=
p
Pressure Formula Manipulation
Multiply both sides by a
f
a*p= *a
a
f = ap
f ap
=
p p
Divide both sides by p
Under Pressure!
1. A Force of 15 Newtons is applied over a
surface area of 0.6m2. What is the pressure?
2. A Force of 25 Newtons is applied over a
surface area of 1.3m2. What is the pressure?
3. A pressure of 50 pascals is pushing down on
an area of 5m2. What is the force?
4. A 20lb box with a length of 10 inches and a
width of inches is resting on the floor. How
much pressure does it exert on the floor?
Pressure, Volume and Temperature: Phet Physics
• What causes pressure in a
balloon?
• Increasing the temperature
of a gas at a fixed volume
does what to pressure?
• Decreasing the temperature
for a fixed volume of gas
does what to pressure?
• Why should you never heat
a closed container?
11
https://phet.colorado.edu/en/simulation/states-of-matter-basics
DANGER Axe Can Fire Baking Soda Rocket
•
Exploding Beer Keg Kills Man
•
NEW MILFORD, Conn. (AP) - October 24, 2006 -Investigators were trying to determine who tossed a beer
keg into a burning barrel at a party, causing a deadly
explosion that sent metal shards slicing through a crowd of
people.
The explosion early Sunday killed Sean M. Caselli, 22, of
New Milford. Seven other people were taken to hospitals
with burns and shrapnel wounds, police said. Caselli was
struck in the neck by a piece of flying metal.
Sgt. Lee Grabner said investigators interviewed witnesses
Sunday to try to identify the person witnesses say threw a
quarter-keg of beer into the flames, and to determine
whether criminal charges should be filed.
Fires had been set in several barrels to keep people at the
partygoers warm at the outdoors party in western
Connecticut, said Police Captain Michael Mrazik.
"This is a certain tragedy," said Police Chief Colin
McCormack. "However, nothing I have been apprised of to
this point in this investigation, which I caution is at the
very early states, indicates a deliberate act on anyone's
part."
(Copyright ©2013 by The Associated Press. All Rights
Reserved.)
•
•
•
•
•
12
Properties of Gas and Gas Laws
•
•
•
•
•
•
Fills its container
Spreads easily
Mix well (e.g. air)
Low Density
Compressible
Mostly empty space
13
Gas in a Container
Boyle’s Law
Gay-Lussac’s Law
Charles’ Law
Constant Temperature
Constant Volume
Constant Pressure
14
Gas Law Summary
Boyle’s Law
Gay-Lussac’s Law
Charles’ Law
Constant Temperature
Constant Volume
Constant Pressure
As V↑P↓ As V↓P↑
As T↑P↑ As T↓P↓
As T↑V↑ As T↓V↓
15
Boyle’s Law
• For a fixed amount of gas
at constant temperature:
• A Volume increases,
pressure decreases.
• As volume decreases,
pressure increases.
• P1V1 = P2V2
PHET PHYSICS APP
16
Gay-Lussac’s law
• For a fixed volume of gas :
• As temperature increases
Pressure increases.
• As temperature decreases
Pressure decreases.
• P1/T1 = P2/T2
PHET PHYSICS APP
17
Charle’s Law
• For a fixed amount of gas
at constant pressure :
• As Temperature
increases, volume also
increases.
• As Temperature
decreases, the volume
also decreases.
• V1/T1 = V2/T2
PHET PHYSICS APP
18
Fluid Pressure!
Why does your head hurt when you swim down deep in a pool?
POOL
The weight of the water pushing down on you creates pressure. The
further down you go, the more water that is above you.
Your head hurts when you dive down in
a pool because of the weight of the
water above you.
20
What happens to air pressure
as you climb a mountain?
Why do mountain climbers use
supplemental oxygen? What is
meant by thin air?
As you go up there is
less air above you
pushing down on you so
air pressure decreases.
The density of air decreases as you go up. There is less
and less of it because gravity pulls it close to the earth.
EARTH
Air Pressure is measured
with a Barometer
Current Pressure
Surface Map
The higher the air
pressure the higher
the mercury rises.
Vacuum
The weight of
the air pushes
down on the
liquid mercury.
The mercury
is forced up
the column.
Current Pressure
• In colder weather the air
pressure on the earth’s
surface is (higher| lower).
Why?
• In warmer weather the air
pressure on the earth’s
surface is (higher| lower).
Why?
Isopleths: contour lines (isobars)
NWS Lab
Objective
Using a black colored pencil, lightly draw lines connecting identical values of sea level pressure. Remember, these lines,
called isobars, do not cross each other. Isobars are usually drawn for every four millibars, using 1000 millibars as the
starting point. Therefore, these lines will have values of 1000, 1004, 1008, 1012, 1016, 1020, 1024, etc., or 996, 992,
988, 984, 980, etc.
Procedure
Label each isobar with the appropriate value. Traditionally, only the last two digits are used for labels. For example, the
label on the 1024 mb isobar would be 24. A 1008 mb isobar would be labeled 08. A 992 mb isobar will be labeled 92.
These labels can be placed anywhere along the isobar but are typically placed around edges of the map at the end of
each line. For closed isobars (lines that connect) a gap is placed in the isobar with the value inserted in the gap.
Analysis Isobars can be used to identify "Highs" and "Lows". The pressure in a high is greater than the surrounding air.
The pressure in a low is lower than the surrounding air.
•
Label the center of the high pressure area with a large blue "H".
•
Label the center of the low pressure area with a large red "L".
High pressure regions are usually associated with dry weather because as the air sinks it warms and the moisture
evaporates. Low pressure regions usually bring precipitation because when the air rises it cools and the water vapor
condenses.
•
Shade, in green, the state(s) would you expect to see rain or snow.
•
Shade, in yellow, the state(s) would you expect to see clear skies..
In the northern hemisphere the wind blows clockwise around centers of high pressure. The wind blows
counterclockwise around lows.
•
Draw arrows around the "H" on your map to indicate the wind direction.
•
Draw arrows around the "L" on your map to indicate the wind direction.
Finished Product: NWS
Contour Maps of CT Mountains
CT Lakes and Ponds
Air always moves from high pressure to
low pressure in an attempt to equalize.
• When you go to the beach during
the day, what is hotter, the sand or
the water?
• When you go to the at night, what
can you tell me about the water
temperature?
Different materials heat up and
cool down at different rates. Water
takes a long time to heat up and a
long time to cool down.
Image via cmap
• During the day the sand is really hot and the water is cool.
• This leads to low pressure and rising air over the land and cold sinking air
over the water.
• As the air on the sand rises air from the oceans moves in and fills it in.
Sea Breeze Cycle
Image via
• At night the sand cools really quickly but the water is comparatively warmer
since it takes far longer to cool off.
• This leads to lower pressure and rising air over the water and cold sinking air
over the land.
• As the air over the water rises air from the land moves in and fills it in.
Land Breeze Cycle
Image via
noaa
Demos to Explain
Demos to Explain
• Paint Stick and Newspaper
• Balloon and Flask
• Egg and Bottle
• Water stuck in a straw
• Dart stuck on the board
• Olive Oil Can
• Can and Ice (Phet)
Pressure on a Balloon
Air Pressure from the
atmosphere is pushing in.
Air Pressure from the
compressed air inside the
balloon is pushing out.
If you remove the
atmospheric pressure the
balloon expands. As a balloon
rises it gets bigger.
Increasing atmospheric
pressure will compress the
balloon.
Lets put a balloon in a vacuum pump!
34
Pressure on a Balloon
Air Pressure from the
atmosphere is pushing in.
Air Pressure from the
compressed air inside the
balloon is pushing out.
If you remove the
atmospheric pressure the
balloon expands. As a balloon
rises it gets bigger.
Increasing atmospheric
pressure will compress the
balloon.
35
Your ear is like a balloon
Why Do Ears Pop?
On the surface of the earth
the pressure in your air
balances with the air
pressure outside of it. As
you ascend in a plane the
outside air pressure lowers
but the pressure remains
the same in your ears. It is
pushing with a higher force
and fortunately, it pops to
release the extra pressure…
36
What Happens to a Bubble blown
underwater? Why?
http://www.youtube.com/watch?v=sn67vDBiL04
37
Why is it easier to Boil Water on a mountain?
Air Pressure!
If you remove or decrease air
pressure boiling water will be much
easier. Thus water boils quicker in
Denver (think Mile High City!).
When we heat liquid water it will
evaporate and enter the air as a gas.
But there is air pressure pushing
down on it which makes it harder
for the water molecules to leave.
If you go up high enough to where the
pressure is very low, your saliva will boil on
tongue due only to the reduced pressure.
38
Is the glass half empty of half full?
50% Air
50% Water
100% Full!!!
Air Pressure
Air has mass so air has
weight or air exerts a
force on us.
Since air exerts a force on
us, there is air pressure.
Measure the surface area
of your smartphone and
calculate the weight of air
pushing down on it
assuming there is 14.7lbs
of pressure per every
square inch.
Do the same for a table in
the room.
Why aren’t we crushed
by this pressure?
40
We aren’t crushed because
Pressure acts in all Directions
There is air in our bodies and it pushes out with the same
pressure that the atmosphere is trying to crush us with
41
Pressure acts in all
directions on an object
submerged in water.
Submarines actually
compress (get smaller) as
they dive deep. If they get
too deep, SNAP, CRACKLE
AND POP!!!
In Casa A you have a string hung tightly
from one side of a submarine to the
other. If the submarine that was initially
at the surface and descends 2000ft, what
happens to the string?
In Casa B you have a string hung tightly
from one side of a submarine to the
other. If the submarine is initially at a
depth of 2000ft and rises to the surface,
what happens to the string.?
SAGS
SNAPS
Cross-Sectional View of a Submarine
Air Pressure vs Water Pressure
Air Pressure
Air Pressure and Water
Pressure balance when
the top is on!
Hole
Olive Oil
Air Pressure
Water Pressure due to the
weight of the water above.
Air Pressure
44
Air Pressure vs Water Pressure
Air Pressure
Hole
Olive Oil
Air Pressure
Water Pressure due to the
weight of the water above
and air pressure from above.
Water comes out when
the top is off! Since the
container is no longer
sealed not only is the
weight of the water
pushing down but the
weight of air in our
atmosphere is pushing
down on it as well.
Air Pressure
45
Is there Air Pressure in Outer Space?
Nasa.gov
46
Three Demos to Explain
• Coke Can in Ice Water
• Heated Flask with Baloon
• Egg in a Bottle
Pressure increases with Depth
–
kg/m3 (water = 1000kg/m3)
• g = gravity (9.8m/s )
• h = height (meters from surface)
Surface
A
2
• Where is the pressure
the greatest? A,B or C.
B
POOL OF WATER
C
Pressure Increases
• P = pgh
• p = density (rho)
48
Hydrostatic Equilibrium: Derivation
•
•
•
•
•
•
•
P = F/A [Force is weight of the fluid]
P = weight/A [weight = mg]
P = mg/A [D = m/V so m = DV]
P = DVg/A [V = LxWxH and A = LxW
P = Dg (LxWxH) / (LxW) [the LxW cancels]
P = Dgh [ we use p instead of D]
P = pgh
49
•
•
•
•
P = pgh
p = density (rho)
– kg/m3
– (water = 1000kg/m3)
– (salt water = 1040kg/m3)
Hydrostatic-Problems
g = gravity (9.8m/s2)
h = height (meters from surface)
1. In 1960 two men aboard the Trieste dove down to
the deepest part of the ocean in the Marianas
Trench in the Pacific Ocean. The reached a depth of
over 10,911 meters. Calculate the pressure in pascals
pushing down on the top of the submarine at that
depth.
2. What is the pressure on a person’s head if she dives
down 30 meters in a lake filled with fresh water?
3. What is the pressure on a submarine if it dives down
1000 meters in salt water.
4. At what depth in a pool of fresh water would a
person experience a pressure of 29,400 pascals? 50
P1
P2
P4
P3
P6
P7
P5
Imagine these are all very deep, very oddly
shaped swimming pools. You have a pressure
sensor and are going to determine the pressure at
all seven locations. In which location(s) is pressure
the smallest? In which is it the greatest? Rank
them in order of smallest to highest pressure.
Computer Lab Clicker Questions
Lowest Pressure
1
2
3
4
5
6
7
Highest Pressure
52
Bernouilli’s Principle
• As the Speed of a
moving fluid increases,
the pressure of the
moving fluid decreases.
• S P
Siphoning Demo
53
Awesome Fluid Dynamics Demos That
Are Not Bernoulli’s Principle
A wing is shaped so that air
traveling over the top of it
has a longer path and moves
faster. This means there is
lower Pressure above a wing
and higher pressure below
it. This is called Lift!
54
Pascal’s Principle and Hydraulics
55
What happens when you squeeze a tube of toothpaste?
Pascal’s Principle: A Change in pressure at any point in
an enclosed fluid will be transmitted equally to all
parts of the fluid.
56
What happens when you squeeze a tube of toothpaste?
P1 = P2
P2
P1
Pascal’s Principle: A Change in pressure at any point in an
enclosed fluid will be transmitted equally to all parts of the fluid.
57
What happens when you squeeze a tube of toothpaste?
P1 = P2
F2 /A2
F1 /A1
Pascal’s Principle: A Change in pressure at any point in an
enclosed fluid will be transmitted equally to all parts of the fluid.
F1 /A1 =F2 /A2
58
Hydraulic Device
A Small amount of Force can lift a very heavy object.
59
Hydraulic Device
F1 /A1 = F2 /A2
60
Pascal’s Principle Problem #1
• A Hydraulic lift uses
Pascal’s principle to lift
a 19,000N car. If the
area of the small piston
is (A1) equals 10.5cm2
and the area of the
large piston (A2) equals
400cm2, what force
needs to be exerted on
the small piston to lift
the car?
F1 / A1 = F2 /A2
61
Pascal’s Principle Problems
1. If a force of 100lbs is applied to
the small piston (A1) which has
an area of 12in2 and the area of
the large piston (A2) is 300in2,
how heavy of an object can be
lifted?
2. A Hydraulic lift uses Pascal’s
principle to lift a 4000lb car. If
the area of the small piston is
(A1) equals 4in2 and the area of
the large piston (A2) equals
65in2, what force needs to be
exerted on the small piston to lift
the car?
F1 / A1 = F2 /A2
62
Hydraulic Brakes / Air Matresses