Transcript Fluid pressure
A. Def – the amount of force exerted over
1. Tires – gases push on the outside
walls of tires
B. Formula P=F/A
C. Measured in Pascals (N/m2)
1. 101.3 kPa at Sea level
2. 1000 Pa = 1 kPa
D. Our Atmosphere
1. Gas layer that covers the earth.
2. Perfect amount of gases
a. Nitrogen – 78%
b. Oxygen – 21%
c. Carbon Dioxide - .04%
d. Water vapor, dust, argon
3. Air pressure ↓’s as altitude increases
E. A book has a force of 30 Newton's while
resting on a table. If the area of the book
is 0.06 m2, how much pressure does the
30 N / 0.06 m2
= 500 Pa
Or 0.5 kPa
Thursday, October 15, 2015
If the air inside a balloon exerts a force of
1.5 N on an area of 0.5 m2, what is the
pressure inside the balloon?
“Forces and Pressures in Fluids”
I can describe how pressure is transmitted
throughout a fluid according to Pascal’s
I. Pascal’s Principle
A. Def – a pressure applied to a fluid is
transmitted throughout the whole fluid.
1. Squeezing toothpaste
2. Squeezing one end of a
B. Hydraulic Machine – uses oil like liquid to
multiply input force up to 10x.
Fluids at Rest - Hydrostatics
II. Bernoulli’s Principle
A. Def – as the velocity of a fluid increases,
the pressure of the fluid decreases.
1. Ex: blowing 2 ping pong balls.
2. Airplanes (pg. 213)
High to Low causes lift for an airplane
As the airplane speeds down the runway,
air rushes over and under the wings. The
air, going over the wings, goes faster and
faster, there is less and less pressure
above the wings. Soon there is much more
pressure below the wings than above. This
pressure pushes up on the wings and the
airplane is lifted into the sky.
3. Venturi Effect
a. Def – reduced air pressure outside
of skyscrapers has caused windows to be
13.2 Assignment: Write a paragraph for why
a “curve ball” in baseball demonstrates the
Friday, October 16, 2015
Describe how pressure is transmitted
throughout a fluid according to Pascal.
I can explain the relationship between the
volume of fluid displaced by an object and
buoyant force acting on the object
according to Archimedes’ principle.
What Archimedes realized about buoyancy Archimedes solved
many problems for King Heiro of Syracuse. His most famous
solution is associated with Heiro's new crown. Heiro had given the
goldsmith the exact amount of gold needed for the crown. After it
was made, Heiro suspected that it might not have as much gold as it
was supposed to. King Heiro summoned Archimedes, and
Archimedes was bewildered with the king's problem. But later, when
Archimedes got into his full bathtub, it occurred to him that the
volume of water that spilled out of the tub was equal to the volume
he displaced. Reasoning that a much lower volume of water would
be displaced by something denser (like gold) even though of equal
weight, he saw the answer to the king's problem. The next day
Archimedes told they king of his discovery. Archimedes put the
king's new crown in a tub of water and found that the crown indeed
displaced more water than the same weight of gold (it occupied
more volume because it had been adulterated with lower density
silver). The goldsmith was immediately beheaded.
A. Def – the ability of a fluid to exert an upward
force on an object placed in it.
1. results in an apparent loss of
easy to lift
opposite of gravity
1. Archimedes's Principle
the buoyant force on an object is
equal to the weight of fluid displaced
by the object.
C. Two Ways to tell if an object can float
> 1 … sink
< 1 … float
2. Force Analysis
weight vs. buoyant force
weight > buoyant force =
weight < buoyant force =
States that the buoyant force on an
object in a fluid is equal to the weight of
the fluid displaced by the object.
Same mass of
Since hull displaces
more water, the
buoyant force is
greater. It floats.
weight = buoyant force