Transcript of Pressure Pressure is equal to the force applied to a surface, divided by the area.
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- Pressure Pressure is equal to the force applied to a surface,
divided by the area.
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- Equations for Pressure Pressure = Force/surface area Pressure =
Newtons (Kg x m/s/s) side x side Units are in Pascals or N/m
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- A substance that can easily change shape or flow. (example:
liquids and gases) The molecules in a fluid have a certain amount
of force (mass & acceleration) and exert pressure on surfaces
they touch
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- All the molecules add up together to make up the force exerted
by the fluid.
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- Air has a mass of 1Kg/m Gravity creates an air pressure of
10.13N/m at sea level.
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- 1 atmosphere = 760 mmHg = 29.92 inHg = 14.7 lb/in2 = 101.3
KPa
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- Air Pressure decreases as elevation increases
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- Very Low pressure Higher Pressure The whole system is a low
pressure, but it dramatically decreases towards the eye of the
hurricane. Pressure always flows from high to low, which creates
the high velocity winds.
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- -A Barometer is used to measure atmospheric pressure. - It can
measure the pressure exerted by the atmosphere by using water, air,
or mercury. -Some types of Barometers are water-based, Mercury,
Barographs and Aneroid. -A barometer is commonly used for weather
prediction, as high air pressure in a region indicates fair weather
while low pressure indicates that storms are more likely.
-Evangelista Torricelli, who is generally credited with inventing
the barometer, went on to build the first instrument with mercury
in 1643.
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- Barometric Pressure The barometer is used to forecast weather.
Decreasing barometer means stormy weather and an increasing
barometer means warmer weather. MERCURY BAROMETERMERCURY
BAROMETER
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- Aneroid vs. Mercury Barometer
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- Water pressure increases with depth.
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- Water Pressure and Depth Water pressure acts in the opposite
direction compared to air pressure Water pressure increases as
depth increases!
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- When a force is applied to a confined fluid, the increase in
pressure is transmitted equally to all parts of the fluid.
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- Transmitting Pressure in a Fluid When force is applied to a
confined fluid, the change in pressure is transmitted equally to
all parts of the fluid.
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- Hydraulic Devices In a hydraulic device, a force applied to one
piston increases the fluid pressure equally throughout the
fluid.
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- Hydraulic Devices By changing the size of the pistons, the
force can be multiplied.
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- 4 N.002m2 20m 1. What is the pressure of the left piston? 2.
What is the pressure of the right Piston? 2000Pa P= F/a = 4/.002 =
2000Pa 3. What is the total force of the right Piston? 40,000NF=Pa=
2000N/m2 x 20m2 =
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- Hydraulic Brakes The hydraulic brake system of a car multiplies
the force exerted on the brake pedal.
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- The tendency or ability of an object to float.
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- Buoyancy The pressure on the bottom of a submerged object is
greater than the pressure on the top. The result is a net force in
the upward direction.
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- Buoyant Force The upward force exerted by a fluid on a
submerged or floating object.
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- Buoyancy The buoyant force works opposite the weight of an
object.
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- Archimedes principle: Buoyant Force acting on an object
immersed in a liquid equals the weight of the liquid displaced and
the weight of the object if it floats. This force does not depend
on the weight of the object!
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- Archimedes' Principle Hmm! The crown seems lighter under water!
The buoyant force on a submerged object is equal to the weight of
the liquid displaced by the object. For water, with a density of
one gram per cubic centimeter, this provides a convenient way to
determine the volume of an irregularly shaped object and then to
determine its density
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- Density and buoyancy: An object that has a greater density than
the fluid it is in, will sink. If its density is less than the
fluid it will float.
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- A solid block of steel sinks in water. A steel ship with the
same mass floats on the surface.
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- Density Changes in density cause a submarine to dive, rise, or
float.
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- Density Changes in density cause a submarine to dive, rise, or
float.
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- Density Changes in density cause a submarine to dive, rise, or
float.
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- 1g/cm
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- The pressure exerted by a moving stream of fluid is less than
its surrounding fluid.
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- Therefore, as the speed of the fluid increases its pressure
decreases.
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- A non-spinning baseball or a stationary baseball in an
airstream exhibits symmetric flow. A baseball which is thrown with
spin will curve because one side of the ball will experience a
reduced pressure. This is commonly interpreted as an application of
the Bernoulli principle. The roughness of the ball's surface and
the laces on the ball are important! With a perfectly smooth ball
you would not get enough interaction with the air. Bernoullis and
Baseball
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- The air across the top of a conventional airfoil experiences
constricted flow lines and increased air speed relative to the
wing. This causes a decrease in pressure on the top according to
the Bernoulli equation and provides a lift force. Aerodynamicists
(see Eastlake) use the Bernoulli model to correlate with pressure
measurements made in wind tunnels, and assert that when pressure
measurements are made at multiple locations around the airfoil and
summed, they do agree reasonably with the observed lift. Bernoulli
equation Bernoullis and Air Foil
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- Others appeal to a model based on Newton's laws and assert that
the main lift comes as a result of the angle of attack. Part of the
Newton's law model of part of the lift force involves attachment of
the boundary layer of air on the top of the wing with a resulting
downwash of air behind the wing. If the wing gives the air a
downward force, then by Newton's third law, the wing experiences a
force in the opposite direction - a lift. While the "Bernoulli vs
Newton" debate continues, Eastlake's position is that they are
really equivalent, just different approaches to the same physical
phenonenon. NASA has a nice aerodynamics site at which these issues
are discussed.angle of attackboundary layer downwash of air