Forces in Fluids

1
Forces in Fluids
2
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)

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
Pressure on a Diver
6
(No Transcript)
7
(No Transcript)
8
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

9
Weather systems
10
Pascals Principle

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

11
(No Transcript)
12
(No Transcript)
13
How it works
Air Pressure
Handle
Handle
Vacuum
Air Tight Seal
14
hydraulics

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

15
Hydraulic Brakes
16
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?

17
Bernoullis principle

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

18
Airplane forces
19
Why is wing shaped the way it is?
20
Other applications of Bernoullis principle
21
buoyancy

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

22
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

23
Archimedes

• The Story

24
Application of buoyancy

• Ballast tanks in submarines

25
submarine fish
26
Density Review

• Density- the amount of matter in a space
• DM/V
• 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?