Lecture 32

Summary

Pressure in fluids
Pascal's principle
Archimedes's principle

three demonstrations of Bernoulli effect

Continuity equation

Example #1

Bernoulli's principle

Image from Hyperphysics

Practice question

Example #6

Lift on an aircraft: NASA web site and applet

Flaps on the trailing edge of a wing increase lift at low speed by deflecting
more air downward. They also generate more drag and cannot be used at
high speed. Image from Wikimedia Commons

bald eagle wing illustrates aerodynamic lift

The eagle's right wing (at left in photo) generates more lift than the left wing
at this instant by deflecting more air downward. Downward force on the air
produces an upward force on the wing, evident especially at the wing tips.
Image © Tom Grey

PoP5 15.41b
A 2.00-cm-diameter hose carries water at 1.06 m/s. With what speed does the water exit a 1.00-cm-diameter nozzle?
A. 1.06 m/s
B. 2.12 m/s
C. 4.24 m/s
D. 0.265 m/s
Answer

kw4 tb
Which of the following does NOT involve the Bernoulli effect?
A. Roof removal by hurricane winds.
B. The rising of a hot air balloon.
C. The lift produced on airplane wings.
D. The curved motion of a baseball pitch.
Answer

Walker4e
Prairie dogs build one entrance of their tunnel higher than the other because the wind speed is higher with increasing altitude. This causes _____ pressure at the high entrance when compared with the low entrance. Walker4e figure 15-20 prairie dog burrow

Walker4e figure 15-20 prairie dog burrow

A. a higher
B. a lower
C. the same
D. an oscillating
Answer

PoP5 Context4.04
A 2.00-N force pushes a syringe plunger of cross-sectional area A = 25.0 mm² and forces water out an a = 0.010 mm² needle. What is the speed of the exiting water?
A. 12.6 m/s
B. 9.33 m/s
C. 160 m/s
D. 58.2 m/s
water in a syringe

Answer

PoP5 15.39
A hole is punched at height h in the side of a container of water full to depth h₀. What should h be to maximize the horizontal range? water container with spigot

A. h₀
B. h₀/2
C. h₀/3
D. h₀/4
Answer

gc6 10.51
By what factor will your garden watering time be cut if you switch from a 3/8 inch diameter hose to a 5/8 inch hose? Reduced constriction in the hose allows the flow velocity to increase by a factor of 2.78.
A. 7.72
B. 2.78
C. 1.67
D. 1.50
Answer

answer

C. 4.24 m/s
solution equation

answer

B. The rising of a hot air balloon.
Hot air balloons rise due to Archimedes' principle.

answer
Walker4e figure 15-20 prairie dog burrow

B. a lower

Bernoulli's principle states that the pressure is least where the speed is greatest. Therefore, the pressure at the higher entrance, where the wind speed is greatest, is lower than the pressure at the entrance at the low end. Fresh air is drawn into the low end of the tunnel and out the high end.

answer
water in a syringe

A. 12.6 m/s
solution equation

answer

B. h₀/2

answer

A. 7.72
solution equation