Chapter 9 Notes

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Announcements : 

Announcements Homework for tomorrow… (Ch. 9, Probs 74 & 77) Office hours… MTWRF 11-noon

Chapter 9 : 

Chapter 9 Fluids

Fluids… : 

Fluids… Includes both gases and liquids Some useful physical quantities

Section 9.3:Density and Pressure : 

Section 9.3:Density and Pressure Density “rho” What are the SI units?

Some Densities… : 

Some Densities…

Pressure : 

Pressure Pressure, P, is the magnitude of the force exerted perpendicular to a given surface What are the SI units? Other units:

Demo: Bed of Nails : 

Demo: Bed of Nails How much weight is on each nail?

Some Pressures… : 

Some Pressures…

Section 9.4: Variation of Pressure with Depth : 

Section 9.4: Variation of Pressure with Depth Hydrostatics How much pressure is on your head? “Fluid” “at Rest”

Depth Dependence of Pressure : 

Depth Dependence of Pressure h P P0 Absolute Pressure, P Gauge Pressure, P - P0

Quiz Question 1 : 

Quiz Question 1 The pressure at the bottom of a 4 m deep swimming pool is: 0.4 atm 0.8 atm 1.2 atm 1.4 atm 4.0 atm

Problem 1 : 

Problem 1 A collapsible bag contains glucose solution. If the average gauge pressure in the blood vessel is 13.3 kPa, what must be the minimum height h of the bag in order to infuse glucose into the artery. Assume that the density of the solution is 1.02 g/cm3: 0.3 m 1.3 m 2.1 m 13.0 m 13.6 m

Pascal’s Principle : 

Pascal’s Principle A change in pressure applied to an enclosed fluid is transmitted to every point of the fluid and to the walls of the container without diminishing

i.e. Hydraulic Press : 

i.e. Hydraulic Press F = ? N A = 10 mm2 A = 10,000 mm2 10,000 N

Barometer : 

Barometer h P = 0 P0

Quiz Question 2 : 

Quiz Question 2 Several common barometers are built using a variety of fluids. For which fluid will the column of fluid in the barometer be the highest Mercury ( = 13,600 kg/m3 ) Water ( = 1,000 kg/m3 ) Ethyl alcohol ( = 806 kg/m3 ) Benzene ( = 879 kg/m3 )

Demo: Crush the Can : 

Demo: Crush the Can Estimate the force on the can by the atmosphere…

Section 9.6: Buoyant Forces and Archimedes’s Principle : 

Section 9.6: Buoyant Forces and Archimedes’s Principle Archimedes of Syracuse (287 B.C. - 212 B.C.) Greek Mathematician, Physicist, and Engineer History: “Bathtub epiphany”

Archimedes’s Buoyancy Principle : 

Archimedes’s Buoyancy Principle Q: Why do things feel lighter underwater (or even float)? Imagine a block in a fluid… h1 h2 F1 F2 h P1 P2

Archimedes’s Buoyancy Principle : 

Archimedes’s Buoyancy Principle The buoyant force is equal to the weight of the fluid displaced.

Quiz Question 3 : 

Quiz Question 3 Imagine holding two identical bricks under water. Brick A is just beneath the surface of the water, while Brick B is at a greater depth. The force needed to hold Brick B in place is larger the same as smaller than the force required to hold Brick A in place.

i.e. Ice Cube : 

i.e. Ice Cube How much of the ice cube’s mass is below the surface of the water? d L

Problem 2 : 

Problem 2 A tin can has a volume of 1000 cm3 and a mass of 100 g. Approximately how many grams of lead shot can it carry without sinking in water: 100 900 980 1000 1100

Quiz Question 4/Demo : 

Quiz Question 4/Demo A boat carrying a large boulder is floating on a lake. The boulder is thrown overboard and sinks. The water level in the lake (with respect to the shore) rises. drops. remains the same.

Section 9.7: Fluids in Motion : 

Section 9.7: Fluids in Motion Ideal Fluids Incompressible ( = constant) No turbulence (no whitewater) Non-viscous (water, not syrup)

Question : 

Question Imagine the block in an ideal fluid… How does P1 compare with P2 ? How does 1 compare with 2 ? h1 h2 F1 F2 h P1 P2

Fluids in Motion… : 

Fluids in Motion… Hydrodynamics Imagine fluid flowing down a cylindrical pipe… “Fluid” “in motion” A x

Equation of Continuity : 

Equation of Continuity (Volume/s)in = (Volume/s)out A1 A2 v1 v2

Quiz Question 5 : 

Quiz Question 5 A blood platelet drifts along with the flow of blood through an artery that is partially blocked by deposits. As the platelet moves through the partially blocked region, its speed: increases decreases remains unchanged

Human Circulatory System : 

Human Circulatory System

Bernoulli’s Equation : 

Bernoulli’s Equation pressure elevation velocity

i.e. Wind Damage… : 

i.e. Wind Damage… v 1 2

i.e. A Box of Wine… : 

i.e. A Box of Wine… What is the speed of the wine as it comes out of the spout? 1 2

Quiz Question 6 : 

Quiz Question 6 A blood platelet drifts along with the flow of blood through an artery that is partially blocked by deposits. As the platelet moves through the partially blocked region, the surrounding pressure: increases decreases remains unchanged

Quiz Question 7 : 

Quiz Question 7 An ideal fluid is pumped steadily up a vertical pipe with a uniform cross-section. The difference in pressure between points at the top and bottom: is the same as it would be if the fluid were motionless. is greater at higher flow rates than at lower flow rates. is less at higher flow rates than at lower flow rates. does not depend on the density of the fluid. is zero.

Q: How do planes fly? : 

Q: How do planes fly? 2 1 v2 v1 Which is larger, v2 or v1?

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