Forces in Fluids Chapter 13
What is pressure? • The result of a force acting over a given area. • Pressure = Force/Area • What label? • N/m2 • 1 N/m2 is known as a pascal (Pa)
Blaise Pascal • 1623-1662 • French physicist and mathematician • Performed some of the first experiments dealing with pressure
Fluid pressure • Fluids: a substance that attains the shape of its container. Examples: both liquids and gases. • Fluid pressure changes with depth in a column of water and with altitude. • Fluid pressure in water does not depend on the volume or weight only the depth.
Air Pressure • Air pressure at sea level is approx. 101 kPa. • Air pressure will decrease with increases in altitude. • Examples: flying in a plane, driving in the mountains
Pascal’s Principle • A change in pressure at any point in a fluid is transmitted equally and unchanged in all directions throughout the fluid
hydraulics • Uses Pascal’s principle and moving pistons with an enclosed pressurized fluid: • Examples: • Car brakes, jacks, and loaders
Problem: • If a force of 30 N is placed on a small piston of a hydraulic device with an area of 2 cm2, what size of a load can the larger piston lift if the area of the larger piston is 80 cm2?
Bernoulli’s principle • Swiss scientist • 1700-1782 • Explained the basis behind airplane flight. • As the speed of a fluid increase, the pressure decreases
buoyancy • The ability of a fluid to exert an upward force on an object resulting in an APPARENT loss of weight of the object
Archimedes • Greek mathematician • 287-212 B.C. • Best known for his theory that the buoyant force on an object is equal to the weight of the fluid displaced
Application of buoyancy • Ballast tanks in submarines
Assignment: • Pages 407-408 • 1-10, 12, 15, 17, 20, 26, 27 • Page 409 • 1-6