Announcements 9/3/10

Any new people? Please see me ASAP.
a.

Class directory printouts
a.


If you missed the signup sheet, I can add you to the list. Send me
an email.
Lab 1 starts tomorrow
No class on Monday! (Labor Day)
a.
b.

If you want to be in class directory and missed the signup sheet, I
can add you to electronic version. Send me an email.
Prayer volunteer list
a.

Josh Asplund & Justin Liu: you are not officially signed up yet
No homework due Monday either!
Homework still due tonight!
Don’t forget about office hours (low HW scores… low office
hour turnout… correlation?)
a.
b.
Mine today are 2-3 pm (in underground lab)
TA’s today are 3-4 pm (also in underground lab)
Clicker quiz

Which do you prefer?
a. (a) White text on black background
b. (b) Black text on white background
This is just a box of fairly random words so that
you can get more of a feel for what black text
on a white background looks like.
(All other slides so far have been the
opposite.)
Thought question (review):

Archimedes was charged with determining if a
crown was pure gold. One method he may have
used: suppose he balanced the crown with pure
gold outside water. After immersing, the balance
tipped as shown. The crown must:
a. Be denser than gold
b. Be less dense than gold
Reading question (graded):

Which of the following is NOT one of
the four assumptions we make when
we model “ideal fluids?”
a.
b.
c.
d.
e.
The
The
The
The
The
fluid is massless
fluid is nonviscous
flow is laminar
fluid is incompressible
flow is irrotational
http://www.youtube.com/watch?v=W3YZ5veN_Bg
Reading quiz (graded):

Water flows from a pipe with large
diameter into a pipe with smaller
diameter. The speed of the water in the
small tube will be _________ the speed
in the large tube.
a. greater than
b. less than
c. equal to
Quick writing assignment

In the reading assignment for today, Ralph
noticed two different equations 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?
Thought questions (ungraded):


Water flows 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
a.
b.
c.
greater than
the same as
less than
a.
b.
c.
d.
e.
1/9
1/3
1
3
9
The speed on the right will be ____ times the speed on
the left.
Airplane Wings

Principle 1: deflection

Principle 2: Bernoulli
http://www.av8n.com/how/htm/airfoils.html
Curve balls

Ball moving to the right (i.e. air moving
to the left), with topspin
Thought question:

A ball is thrown toward you, spinning so that (as
you look at it) the right side of the ball spins
toward you, and the left side away. The ball will
a.
b.
c.
d.
“float” more than a nonspinning ball
“sink” faster than a nonspinning ball
curve to your left
curve to your right