Forces in Fluids

1
Forces in Fluids

• Chapter 13

2
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)

3
Blaise Pascal

• 1623-1662
• French physicist and mathematician
• Performed some of the first experiments dealing
  with pressure

4
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.

5
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

6
Pascals Principle

• A change in pressure at any point in a fluid is
  transmitted equally and unchanged in all
  directions throughout the fluid

7
hydraulics

• Uses Pascals principle and moving pistons with
  an enclosed pressurized fluid
• Examples
• Car brakes, jacks, and loaders

8
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?

9
Bernoullis principle

• Swiss scientist
• 1700-1782
• Explained the basis behind airplane flight.
• As the speed of a fluid increase, the pressure
  decreases

10
Airplane forces
11
Why is wing shaped the way it is?
12
Other applications of Bernoullis principle
13
buoyancy

• The ability of a fluid to exert an upward force
  on an object resulting in an APPARENT loss of
  weight of the object

14
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

15
Application of buoyancy

• Ballast tanks in submarines

16
submarine fish
17
Assignment

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