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PHYS16 – Lecture 31
Fluids: Bernoulli’s Principle November 12, 2010
What is Google really trying to say?
No Seriously!!
Outline for Fluids
• Pressure and Pascal’s Principle• Buoyant Force and Archimedes’ Principle• Fluid dynamics– Ideal Fluids– Equation of Continuity– Bernoulli’s Equation
Bernoulli’s Equation
• For an ideal fluid flowing in a pipe, pressure in the pipe is related to the velocity and height of fluid
2222
2111 2
1
2
1vghpvghp
Example: Blood Pressure
• What would happen if the doctor took a blood pressure reading at the wrist instead of on the bicep?
A) Blood pressure would be higherB) Blood pressure would be lowerC) Blood pressure would be the same
http://www.omron.com
Example: Aneurysm
• In an aneurysm the arterial wall weakens and the diameter increases. Why does this increase the chance of rupture?
http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/18072.jpg
A increases, v decreases, P increases
Example: Draining Water
• What happens when you drain a bottle of water?
As water height decreases,speed at bottom decreases
Example: Water jets out of a bottle
• Which jet will have the largest range?
12345
What is wrong with this cartoon?
On a windy day in 1735, a new wig gives Bernoulli an idea.
Wind is blowing in the wrong direction…
What happens if fluid is not ideal?
Poiseuille's Law
• When frictional forces dominate velocity decreases– Viscous fluids– Small Diameters
Ideal – larger diameters With Friction – small diameters
p
v
2
L
prv
8
2
Main Points
• Buoyant force
• Ideal fluid is incompressible, laminar, nonviscous, and irrotational
• Equation of continuity
• Bernoulli’s Equation
gVF underwaterobjectfluidB
constant Av
constant 2
1 2 vghp
What’s left…
• 2 online and 2 written homeworks• 1 lab homework• 1 formal lab report• 1 lab• 1 last cumulative exam