QUICK WRITE

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QUICK WRITE
Why is the electricity produced at the bottom of
dams?
When you catch a deep-sea fish, why does its eyes
pop-out?
Why do your ears pop on an airplane or up in the
mountains?
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Forces in Fluids
Chapter 11 Notes
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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/m²

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Fluid

• A substance that can easily change its shape,
  such as liquids and gases.

• The molecules in a fluid have a certain amount of
  force (mass and acceleration) and exert pressure
  on surfaces they touch.

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FLUID PRESSURE

• 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/m³

AIR PRESSURE

• Gravity creates an air pressure of 10.13N/m³ 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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Pressure and Elevation

• Air Pressure decreases as elevation increases.

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The whole system is a low pressure, but it
dramatically decreases towards the eye of the
hurricane.
Very Low pressure
Pressure always flows from high to low, which
creates the high velocity winds.
Higher Pressure
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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.

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START AT 310

• Bill Nye Atmosphere

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Pressure and Depth

• Water pressure increases with depth.

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• c88c.pdf

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Pascal's Principle

• 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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activeart/hydraulic_systems/hydraulic_systems.html
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3. What is the total force of the right Piston?
4 N
40,000N
FPa 2000N/m2 x 20m2
20m
.002m2
1. What is the pressure of the left piston? 2.
What is the pressure of the right Piston?
P F/a 4/.002 2000Pa
2000Pa
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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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Buoyancy
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 on an object immersed in a liquid
  equals the weight of the liquid displaced and the
  weight of the object if it floats.

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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.

Density
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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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DENSITY OF WATER
1g/cm³
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Bernoulli's Principle
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Bernoulli's Principle

• The pressure exerted by a moving stream of fluid
  is less than its surrounding fluid.

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Bernoulli's Principle

• Therefore, as the speed of the fluid increases
  its pressure decreases.

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Bernoullis and Baseball
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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.

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MORE EQUATIONS!!!
Liquid Pressure ?gh where..
? mass/volume fluid density g acceleration
of gravityh height or depth of fluid
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Fluid Pressure ?gh 1000Kg/m³ x 9.8m/s² x 1m
9,800 Pa
Fluid Pressure ?gh 1000Kg/m³ x 9.8m/s² x 3m
29,400 Pa
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Pressure and Temperature

• As temperature increases, pressure increases.