12/19/16
Introduction
•  What is pressure?
Fluid Pressure
Physical Science
pages 390-395
Mr. Schmidt
Physical Science
pages 390-395
Introduction
•  What is pressure?
–  The force exerted on a surface across a
specific area
Introduction
•  When you are standing on the ground.
•  What is the force you are exerting on the
ground?
Physical Science
pages 390-395
Physical Science
pages 390-395
Walking in the snow
Pressure and Area
•  If you walk outside in very deep snow,
chance are you will sink into the snow
•  What can be done to help reduce the
pressure exerted?
Physical Science
pages 390-395
•  As the area over which the force is
applied increases, pressure decreases
Physical Science
pages 390-395
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Pressure and Area
•  How does a bed of nails work?
Calculating Pressure
Pressure =
• 
• 
• 
• 
• 
Force
Area
Physical Science
pages 390-395
STP
Changes in Pressure
–  A measure of the temp and pressure of a gas
F
A
Force is measured in Newtons (N)
Area is measured in square meters (m2)
Pressure is in N/m2 or pascal (Pa)
1,000 pascals is a kilopascal (kPa)
May also be measured in atm, Torr, or psi.
Physical Science
pages 390-395
•  Standard Temperature and Pressure:
P=
•  What happens to pressure in your head as
you are swimming and dive deep?
•  Pressure: 1 atm
•  Temperature: 0°C or 273.15 K
Physical Science
pages 390-395
Physical Science
pages 390-395
Changes in Pressure
HW
•  What happens to pressure as you go up in
altitude?
Physical Science
pages 390-395
•  Answer Questions 1-9 on page 393.
•  Due Tomorrow, 12/20.
Physical Science
pages 390-395
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12/19/16
Pascal’s Principle
Hydraulic Systems
•  When force is applied to a confined fluid,
the change in pressure is transmitted
equally to all parts of the fluid.
Pressure =
Force
Area
Physical Science
pages 390-395
Physical Science
pages 390-395
Using Pascal
Pascal’s Principle
•  Pascal’s Principle
– pressure applied to a fluid is
transmitted unchanged throughout the
fluid
View hydraulics explanation.
F1 F2
P=
A1 A
A2
Physical Science
pages 390-395
Pascal’s Principle
Bernoulli’s Principle
•  A car weighing 1000 N sits on a 250 m2 platform.
What force is needed on the 10 m2 plunger to keep the
car from sinking?
F1 F2
=
A1 A2
•  Bernoulli’s Principle
– as the velocity of a fluid increases, the
pressure exerted by the fluid decreases
– Ex: airplane lift, curve balls, chimney,
drinking straw
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Bernoulli’s Principle
Airplane lift
Curve Ball
Bernoulli’s Principle
•  Venturi Effect
Bernoulli’s Principle
Funnel Demos
Bernoulli’s Principle
Venturi Effect - Atomizers
– fluids flow faster through narrow
spaces causing reduced pressure
– EX: garden sprayer, atomizer,
carburetor
Archimedes’ Principle
•  Fluid
– matter that flows
– liquids and gases
•  Buoyancy
– the ability of a fluid to exert an upward
force on an object immersed in it
Archimedes’ Principle
•  Buoyant Force
– upward force exerted by a fluid on an
immersed object
– buoyant force > weight
balloon rises
§  buoyant force < weight
balloon sinks
§  buoyant force = weight
balloon floats
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Archimedes’ Principle
Archimedes Principle
•  Archimedes’ Principle
– the buoyant force on an object in a
fluid is equal to the weight of fluid
displaced by the object
Not
More
water
needs
water
is
to displaced
betodisplaced
in order
in order
toorder
cancel
to to
Veryenough
little
water
needs
be displaced
in
cancel ⇒
weight
weight
ball sinks.
⇒ ball floats lower
in the water.
on surface.
Physical Science
pages 390-395
View Buoyancy JAVA Applet.
View animations produced by students at Poly Prep Country Day School in Brooklyn, New York.
•  A company makes garden statues by pouring concrete into a
mold. The amount of concrete used to make a statue of a deer
weighs 3600 N. If the base of the deer statue is 0.60 meters long
and 0.40 meters wide, how much pressure will the statue exert
on the ground? (Hint: Area is equal to length times width.)
Physical Science
pages 390-395
•  The weight of the gasoline in a 55-gallon drum creates a force of 1456
newtons. The area of the bottom of the drum is 0.80 m2. How much pressure
does the gasoline exert on the bottom of the drum?
–  Pressure = Force/Area = 1456 N/0.80 m2 = 1820 Pa = 1.8 kPa
Can you handle the pressure?
answers
•  The weight of a gallon of milk is about 38 N. If you pour 3.0
gallons of milk into a container whose bottom has an area of
0.60 m2, how much pressure will the milk exert on the bottom of
the container?
Can you handle the pressure?
•  The weight of the gasoline in a 55-gallon drum creates a force of
1456 newtons. The area of the bottom of the drum is 0.80 m2.
How much pressure does the gasoline exert on the bottom of the
drum?
•  The weight of a gallon of milk is about 38 N. If you pour 3.0 gallons of milk
into a container whose bottom has an area of 0.60 m2, how much pressure
will the milk exert on the bottom of the container?
–  Force = (3.0 gallons)(38 N/gallon) =114 N;
–  Pressure =Force/Area = 114 N/0.60 m2=190 Pa =0.19 kPa
•  A company makes garden statues by pouring concrete into a mold. The
amount of concrete used to make a statue of a deer weighs 3600 N. If the
base of the deer statue is 0.60 meters long and 0.40 meters wide, how much
pressure will the statue exert on the ground? (Hint: Area is equal to length
times width.)
–  Area = 0.60 m x 0.40 m = 0.24 m2;
–  Pressure = Force/Area = 3600 N/0.24 m2= 15,000 Pa = 15 kPa
Name: _______________________
Physical Science
pages 390-395
Name: _______________________
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