PHYS16 – Lecture 34 Fluids: Bernoulli’s Principle Far side

Outline for Fluids Fluid Statics – Pressure and Pascal’s Principle – Buoyant Force and Archimedes’ Principle Fluid Dynamics – Ideal Fluids – Equation of Continuity – Bernoulli’s Equation

Fluid Dynamics: 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

Discussion: Two sheets in the wind? What happens if I take two sheets of paper, separate them by 1” and blow between them? A) sheets will move apart B) sheets will come together C) sheets will stay at same spots

Discussion: 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 higher B)Blood pressure would be lower C)Blood pressure would be the same

Discussion: Aneurysm In an aneurysm the arterial wall weakens and the diameter increases. Why does this increase the chance of rupture? A increases, v decreases, P increases

Example: Water jets out of a bottle Which jet will have the largest range?

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

Fluids pre-question Salt water has a greater density than freshwater. A boat floats in both freshwater and salt water. The buoyant force on the boat in salt water is _________ that in freshwater. A)Equal to B)Smaller than C)Larger than D)Not enough information

Fluids pre-question You are in a boat filled with large rocks in the middle of a small pond. You begin to drop the rocks into the water. What happens to the water level of the pond? A)It rises. B)It falls. C)It doesn’t change. D)It rises momentarily and then falls when the rocks hit bottom. E)Not enough information

Fluids pre-question A 0.2-kg coke can floats in fresh water (1000. kg/m 3 ). The can is 12 cm long and has a radius of 2.5 cm. What is the buoyant force on the can? A)2.0 N B)2.3 N C)1.8 N D)0.3 N

Fluids pre-question You are watering some flowers with a garden hose. You want to water some flowers in the very back of the garden. Assume that the flowers you want to water are at the same level as the hose. What do you have to do to the opening of the hose to increase the range by 4? A) Decrease the area by a factor of 16 B) Decrease the area by a factor of 4 C) Decrease the area by a factor of 2 D) Increase the area by a factor of 2 E) Increase the area by a factor of 4

Main Points Buoyant force Ideal fluid is incompressible, laminar, nonviscous, and irrotational Equation of continuity Bernoulli’s Equation