Physics fluids - glencoe 13.3

11
3 Fluid Principles Glencoe 13.3

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Transcript of Physics fluids - glencoe 13.3

Page 1: Physics   fluids - glencoe 13.3

3 Fluid PrinciplesGlencoe 13.3

Page 2: Physics   fluids - glencoe 13.3

P = F/A P = ρgh Derive the relationship between these two

pressure equations. Verify both yield Pascals for units.

Pressure

Page 3: Physics   fluids - glencoe 13.3

Pascal’s Principle = Hydraulics

Force is multiplied as a ratio of piston areas.

Page 4: Physics   fluids - glencoe 13.3

Pressure is consistent throughout a fluid.

Liquids are dense and incompressible.

P1 = F1/A1 P2 = F2/A2 P1=P2 Therefore F2 = F1(A2/A1) Force is multiplied as a

ratio of piston areas. NOTE: Trade-off is the

distance pistons travel. The small piston has to move the greater distance, because work (energy) is conserved.

Pascal’s Principle

Image source: How Stuff Works –Hydraulics

Page 5: Physics   fluids - glencoe 13.3

Archimedes found that an object displaces its own volume of the fluid it is in. Another way of saying this is…

Fbuoy = weight of fluid displaced

The buoyant force affects the object’s weight. The apparent weight = weight – buoyant force

Archimedes Principle

Page 6: Physics   fluids - glencoe 13.3

A cube of aluminum (10E-3 m3) is submerged in water.

ρAl = 2.7E3 kg/m3

ρH2O = 1E3 kg/m3

What is the buoyant force? What is the apparent weight?

Sample Problem

Page 7: Physics   fluids - glencoe 13.3

A cube of aluminum (1E-3 m3) is submerged in water.

ρAl = 2.7E3 kg/m3

ρH2O = 1E3 kg/m3

What is the buoyant force? 9.8N What is the apparent weight? 2.7*9.8 –

9.8 = 16.7 N

Sample Problem

Page 8: Physics   fluids - glencoe 13.3

As the velocity of a fluid increases, the pressure exerted by that fluid decreases.

P1 + 1/2 ρ v12  + ρ gh1 = P2  + 1/2 ρ v2

2  + ρ gh2 

W1 + KE1 + PE1 = W2 + KE2 + PE2

Bernoulli’s Principle

Page 9: Physics   fluids - glencoe 13.3

Lift: To maintain equilibrium in a straight and level flight, pilots must monitor the aircraft's speed and pitch angle. Those variables along with other factors are used in a formula to determine an aircraft's lift.

Lift=(1/2)(air density)(velocity)(aircraft's wing area)(coefficent of lift)

Air density decreases with altitude. The coefficent of lift varies with the

aircraft's type of airfoil.

Bernoulli’s Principle

Page 10: Physics   fluids - glencoe 13.3

When fluid moves through constriction, velocity increases so same amount of mass can move through at same time.

A1v1 = A2v2 EQUATION OF CONTINUITY

See ThinkQuest animation: http://library.thinkquest.org/27948/bernoulli.html

Bernoulli’s Principle

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Ideal fluids are continuous, incompressible (therefore, not gases) and have laminar (smooth) flow.

Real fluids are turbulent, experience friction, and have viscosity variation.

Ideal Fluids

Image source: answers.com