Tuesday, June 7, 2011

Announcements:

• Our final exam is scheduled for next Tuesday from 8:00 - 11:00 am.  I will hold an optional review session for the final exam next Monday during our regular class time and also at 12:00 pm on Monday in Phillips 215.
• The format for the final exam will be similar to the midterm exams, but entirely multiple-choice (50 questions), with relatively equal weight given to each chapter.
• I will hold a review session for the Lab Exam tomorrow immediately after class as I have for the other exams.
• Be sure to review the sample lab exam to help you prepare for your lab exam.
• Dmitry will hold an extended SI session on Monday from 5:00 - 7:00 pm in Phillips 220?

Assignments:

• HW15 is due tomorrow night.
• HW16 is due Thursday night

Chapter 15:  Fluids Density = Mass/Volume

Pressure = Force/Area
1 Pa = 1 N/m^2
P = Po + Dgh

Pascal's principle:  Pressure at a given depth is same everywhere in an enclosed fluid.

A net upward buoyant force results from difference in pressures acting on the top and bottom surfaces of an object immersed in a fluid.

Archimedes' principle states that the magnitude of the buoyant force acting on an object is equal to the weight of the fluid displaced by the object.

An object floats when it displaces an amount of fluid equal to its weight.  This occurs when the overall density of the object is less than the fluid in which it is immersed.

The equation of continuity for incompressible fluids is A1v1 = A2v2, which basically means that flow in = flow out.

The equation of continuity for compressible fluids is D1A1v1 = D2A2v2.

Bernoulli's equation is:  P + 0.5Dv^2 + Dgy = constant
Consequence:  Faster fluid flow means lower pressure. (This is how airplane wings produce lift.)

The Reynolds number is a dimensionless factor that indicates whether fluid flow will be turbulent (RN > 3000), streamline (RN < 2000), or somewhere in between.

Viscosity refers to the internal friction of a fluid.  Lower viscosity fluids flow easier than high viscosity fluids.

The rate of flow through a pipe can be found from Poiseuille's Law.  From this equation, we can see that the rate of flow is proportional to the fourth power of the radius, so a small increase in the diameter of a tube will result in a very large increase in the flow rate.

Terminal speed of an object falling in a viscous medium is reached when the magnitude of the frictional resistance equals the weight of the object.

Surface tension: gamma = F/L
Capillary action is a result of surface tension.

Fick's Law can be used to find the rate of diffusion, which is proportional to the concentration gradient and the cross-sectional area between two regions.

Elastic modulus = stress/strain
Stress is proportional to force exerted and has same units as pressure.
Strain is a measure of degree of deformation.
1D - Young's modulus, Y
2D - Shear modulus, S
3D - Bulk modulus, B

Ponderables:

• What determines whether an object floats?
• How much water is displaced by a floating object?
• How much water is displaced by a submerged (sunken) object?
• Does an object weigh more or less in a vacuum?
• How much would you appear to weigh in a vacuum?
• Why does a can of Coke sink, but Diet Coke floats?
• How can you make a bowling ball float?
• How does the Bernoulli blower work?
• A person in a boat floating in a small pond throws an anchor overboard.  Does the level of the pond rise, fall, or remain the same? [fall]
• What happens to the water level in a glass as the ice in it melts? [stays the same]
• What happens to the water level in a glass as the ice (with small pebbles) in it melts? [falls]
• Should a golf ball have backspin or topspin for maximum flight distance? [backspin]
• To make a baseball curve to the left, which way should the pitcher spin the ball? [spin to the left]
• Chicago has been called "the windy city."  How does the Bernoulli effect contribute to this nickname? [air speeds increases as it passes through the narrow spaces between the buildings]
• When your instructor lays on a bed of nails, how much force does each nail contribute to support his weight? [~150 lbs/1500 nails =  0.1 lb/nail]
• If an angioplasty procedure expands an artery too much so that the diameter is significantly larger than the surrounding region, would the blood pressure be larger or smaller at that point?  How is this similar to an aneurism?

Problems:

• How much would a 70.0-kg person "weigh" in a vacuum? [685.1 N]
• What is the maximum weight that the suction square could support (Dia. = 6 in.)?  [400 lbs.]
• You decide to weigh your car by applying the physics you have learned.  Each tire is inflated to 35 psi and the area in contact with the road is about 20 sq. in.  How much does the car weigh?  [2800 lbs.]
• What fraction of the total volume of an iceberg is exposed above water?  [10.7%]
• What are the forces on a block of aluminum suspended in water by a spring scale?
• If an aluminum block is suspended in water by a spring scale, and the water is held in a container that rests on another scale, what do the scales read?
• If the outside pressure on the emergency door of an airplane is 0.3 atm, and the door has an area of 6 s.f., what is the net force on the door caused by the pressure difference inside and outside the plane?  How many people would it take to hold the door in place if it were not secured by the door frame?
• Which is more effective for improving the flow rate of blood through an artery:  1)  use of a blood thinner that reduces the blood's viscosity by 50%, or 2) an angioplasty procedure that increases the inside diameter of a clogged artery to twice its original size?  [The flow rate will be 8 times greater for the angioplasty than for the blood thinner.]