1. Fluids
AP/IB Physics

2. Fluids Substances that flow Characteristics Liquid Characteristics
Liquids
Gases
Characteristics
Pressure
Viscosity
Liquid Characteristics
Adhesion & Cohesion
Surface Tension
Capillary Action
Gas Characteristics
Compressibility

3. Fluid Statics Pressure Boyle’s Law Pascal’s Principle
Archimedes’ Principle

4. Pressure Force per unit area
Pascal = N/m2 (english sys: psi)
Results from the weight of the fluid above

5. Pressure Force per unit area
Pascal = N/m2 (english sys: psi)
Results from the weight of the fluid above

6. Pressure Force per unit area
Pascal = N/m2 (english sys: psi)
Results from the weight of the fluid above
pure water
1 L = 1 kg = 9.80 N
1 ft3 = 62.4 lbs
seawater (average)
1 L = 1.03 kg = N
1 ft3 = 64 lbs

7. Pressure Air is 0.1% as dense as water Atmosphere  52 miles high
Pressure at sea level
1 atm = 14.7 psi = 1 kg/cm2 = 1x105 P
1 atm = 10 m of seawater

8. Pascal’s Principle
Pressure exerted in a fluid is the same in all directions

9. Pascal’s Principle Connect a large & small syringe via a plastic tube.
Depress first one plunger then the other.
Which one is easier? Why?
Which one moves farther (in relation to the other)? Why?
Fill the system with water & repeat the experiment.
Why is it very bad to have air bubbles in your car’s brake lines?

10. Pascal’s Principle
Pressure exerted on a fluid in a closed system is the same throughout the system

11. Boyle’s Law Gases Only  Pressure =  Volume  Pressure =  Volume
Pressure exerted on the outside of a gas is inversely proportional to the volume of the gas, if its temperature remains constant.
 Pressure =  Volume
 Pressure =  Volume
P1 = V2
P2 V1

12. Archimedes’ Principle
Weigh a fishing weight using a spring scale.
Weigh it once again, but immersed in water.
What is the buoyant force on the weight?
How much water is displaced by the weight?
What is the weight of the water displaced?
Compare buoyant force to weight of water displaced.

13. Archimedes’ Principle
Any object that is immersed in a fluid, in whole or in part, will be buoyed up by a force equal to the weight of the fluid displaced.

14. Archimedes’ Principle
Buoyant Force
Upward force exerted on an object by a fluid in which it is immersed

15. Archimedes’ Principle
States of Buoyancy
Positive
Neutral
Negative

16. Archimedes’ Principle
An object will sink into a fluid until it displaces an amount of the fluid equal to its own weight.

17. Archimedes’ Principle
Float
Object weighs less than the fluid it displaces
Sink
Object weighs more than the fluid it displaces

18. Fluid Dynamics
Continuity
Bernoulli’s Principle

19. Continuity Equation
A given system of flowing fluid, not gaining or losing fluid
Choose two points – same amount of fluid passes each point in a given time
1A1v1 = 2A2v2

20. Continuity Equation Most gases readily compress, most fluids do not
Equation of Continuity for an Incompressible Fluid
A1v1 = A2v2

21. Bernoulli’s Principle
Work-Energy theorem applied to fluids
Relationship between pressure, speed, & height

22. Bernoulli’s Principle
Work-Energy theorem applied to fluids
Relationship between pressure, speed, & height
General Equation for taking into account changes in height and speed
P1 + ½v12 + gy1 = P2 + ½v22 + gy2

23. Bernoulli’s Principle
Faster moving air exerts less pressure

24. Torricelli’s Law
An application of Bernoulli’s Principle
v2 = 2gh