Fluids AP/IB Physics

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

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

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

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

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 = 10.095 N 1 ft3 = 64 lbs

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

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

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?

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

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

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.

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.

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

Archimedes’ Principle States of Buoyancy Positive Neutral Negative

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

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

Fluid Dynamics Continuity Bernoulli’s Principle

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

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

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

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

Bernoulli’s Principle Faster moving air exerts less pressure

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