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Announcements 8/31/12

Announcements 8/31/12. Prayer Class directory handouts Any new people? Please see me after class.

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Announcements 8/31/12

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  1. Announcements 8/31/12 • Prayer • Class directory handouts • Any new people? Please see me after class. • From syllabus: “If a very large or very small value needs to be written in scientific notation, as specified by the answer range, indicate the exponent of 10 with an “e”. For example, 2.998108 would be written 2.998e8, and 1.610-19 would be written 1.6e-19. Do not put any spaces, commas, or “x”s in the number. Do put in negative signs where appropriate.” xkcd:

  2. From warmup Extra time on? Bernoulli’s equation (5 people) Toricelli’s law (1 person) Other comments? you should maybe show a skydiving clip to show fluid dynamics and how adjusting yourself can adjust where/how fast you go. I'm not sure if you got the first quiz I submitted

  3. Clicker question: Archimedes was charged with determining if a crown was pure gold. One method he may have used: suppose he balanced the crown with a lump of pure gold outside water. After immersing, the balance tipped as shown. The crown must: Be denser than gold Be less dense than gold

  4. Clicker questions: In the demo, what will happen to the upper scale when the mass is submerged. scale reading increases scale reading decreases nothing changes What will happen to the lower scale? scale reading increases scale reading decreases nothing changes Demo: scales

  5. Clicker question: A cannonball is in a boat, which is in the middle of a small lake. (Frictionless, wave-less, etc.) A person tosses the cannonball from the boat into the lake. What happens to the overall water level of the lake (where the water touches the shore)? It rises It falls It stays the same

  6. Worked Problem • An upside-down pyramid (side length s, height h) is placed in a fluid. rpyramid < rfluid, so it floats. In terms of the given quantities and fundamental constants, how far into the fluid does the pyramid settle? (It doesn’t tip.) s h water level y = ? Answer:

  7. Fluid Motion • Disclaimer: We’ll ignore • compressibility • viscosity • turbulence The power of viscosity (watch on your own): http://www.youtube.com/watch?v=W3YZ5veN_Bg

  8. Clicker question: • Water flows from a pipe with large diameter into a pipe with smaller diameter. The speed of the water in the narrow section will be _________ the speed in the wide section. • greater than • less than • equal to • The pressure of the water in the narrow section will be _________ the pressure in the wide section. • greater than • less than • equal to

  9. The Bernoulli Effect • When a constantly flowing fluid has regions of different speed in its flow, the pressure of the fluid will be lowest in regions where the speed is fastest.  What this doesn’t mean… • Why would the fluid change speed?  The “garden hose equation”, aka Eqn of C_____  Terminology: “volume flow rate”

  10. Warmup question 1 Two identical buckets… second one filled while holding your thumb over the end of the hose. How long to fill? The same amount. The volume of water coming out is exactly the same as before, it is merely the speed of the water that has changed.

  11. Warmup question 2 In your own words explain what the "equation of continuity" for fluids means. Audience = brother/sister/mother who hasn't taken physics at all. The equation of continuity is a fancy way of saying what goes in must go out. The same amount of water going into a hose, for example, must go out. Now, if the opening of the hose is larger than the ending of the hose, lots of water is coming in within a second. The equation of continuity states that the same amount of water must come out within the same time period, but since the opening is smaller, it comes out faster.

  12. Demos • Bernoulli red fluid • Chimney effect • Warmup question #3: If the airstream from a hair dryer is directed over a ping pong ball, the ball can be levitated. Explain how this works. • Floating ball • Ball in funnel • Video: Elder Nelson’s spool (start at 1:57, go to ~4:00) • Cards & wooden block • Piece of Paper

  13. Quick writing (random student) • In the reading assignment for today, Ralph noticed two different equations both labeled "Bernoulli's Equation". One said, P1 + ½ rv12 + rgh1 =  P2 + ½ rv22 +rgh2 whereas the other said, P + ½ rv2 + rgh = constant He asks you how they can both be the same equation when they look so different? And what it’s the value of the constant in the second equation, anyway? What should you tell him?

  14. Why does this happen? • View #1: you’re a molecule right there in what direction is the net force? • View #2: energy & work, per volume (yields “Bernoulli Equation”)

  15. Clicker question: • Water flows from right to left, from the little pipe into the big pipe. Ignore any friction or height change. The volume flow rate on the right will be ______ on the left • greater than • the same as • less than • The speed on the right will be ____ times the speed on the left. • 1/9 • 1/3 • 1 • 3 • 9

  16. Demo (not used) Does aluminum sink or float?

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