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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

Pascals Principle

- A change in pressure at any point in a fluid is

transmitted equally and unchanged in all

directions throughout the fluid

hydraulics

- Uses Pascals 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?

Bernoullis 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 Bernoullis 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

Application of buoyancy

- Ballast tanks in submarines

submarine fish

Assignment

- Pages 407-408
- 1-10, 12, 15, 17, 20, 26, 27
- Page 409
- 1-6