Forces in Fluids

What is pressure? The result of a force acting over a given area. Pressure = Force/Area Measured in 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.

Pressure on a Diver

Air Pressure The standard atmosphere (symbol: atm) is a unit of pressure equal to 101325 Pa It is equivalent to 760 mmHg or 14.696 psi. Air pressure will decrease with increases in altitude. Examples: flying in a plane, driving in the mountains

Weather systems

Pascal’s Principle A change in pressure at any point in a fluid is transmitted equally and unchanged in all directions throughout the fluid

Air Pressure How it works Handle Handle Vacuum Air Tight Seal

hydraulics Uses Pascal’s principle and moving pistons with an enclosed pressurized fluid: Examples: Car brakes, jacks, and loaders

Hydraulic Brakes

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

Airplane forces:

Why is wing shaped the way it is?

Other applications of Bernoulli’s principle:

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

Archimedes The Story

Application of buoyancy Ballast tanks in submarines

“submarine” fish

Density Review D=M/V Density- the amount of matter in a space Density of water is 1 g/ml or 1 g/cm3 What is the density of a piece of wood that has a mass of 25.0 grams and a volume of 29.4 cm3?