Equipment (next to red bin containing rotating bodies
Demo):
-small balloon filled with
water
-spring scale with large
dial
-string
-large beaker filled 2/3
with water
[Tie balloon to short
piece of string and weight on
scale (around 5N usually). Ask
students what it should
weigh under water: same, half, double,
nothing?
Lower balloon into water
while attached to scale.
Show that it weighs
nothing. Point: buoyant force
is equal to weight since it has the same
density as water.
Also show that tension in the spring scale
does not depend
on the depth of the balloon in the water,
even though we
know that the pressure increases.
(Darien)]
Bernoulli 1
----------
Equipment:
- dollar bills (2)
[Hold two dollar bills
parallel, about 3 cm apart.
Older (not crisp) bills work
better.
Ask students what will happen when you blow
in between
them? Will they move apart, move
together, stay in
place? When you blow, they should
move together.
Point: Bernoulli says the pressure is lower
where the
air is moving faster.
I've never tried it, but
maybe this could be scaled up
with a couple of towels replacing the
dollar bills and
the weed blower used to move the air
between them.(Darien)]
Bernoulli 2:
Equipment (next to
red bin containing rotating bodies Demo):
-volleyball
-weed-blower.
-----------
[Explain how a ping-pong
ball can be suspended in the
air stream of the vacuum clear
exhaust. (This is in the
lecture notes; air moves faster at the
center of the
stream, so there is a pressure minimum
which traps the
ball). Start with the weedblower
aimed straight upward.
Have a student volunteer place a volleyball
in the middle
of the air stream where it is stable.
Slowly tilt the
weedblower toward horizontal. You
should be able to get
to about 45 degrees before the ball
falls. It should sit
about a meter from the nozzle, so the
effect is quite
dramatic. Point: pressure is lower
where the fluid is moving
faster.
Careful not to aim the
weedblower toward any loose papers.(Darien)]