Done by:

1
Pressure

• Done by
• Andrew Ong 3P316

2

• The symbol for Pressure is P ( Pascal)
• Definition The force per unit area applied in a
  direction perpendicular to the surface of an
  object .

3

• The SI unit for pressure is the Pascal (Pa),
  equal to one Newton per square meter.
• This special name for the unit was added in
  1971 before that, pressure in SI was expressed
  simply as N/m2.

4

• One example which shows the application of
  pressure can be seen in a knife. By cutting a
  fruit with the flat side of the knife, we are
  unable to cut the fruit.
• However, if we use the thin side of the knife to
  cut the fruit, we are able to cut it easily. This
  is because the flat side has a greater surface
  area, which means less pressure, and hence is
  unable to cut the fruit. However, when using the
  thin side, the surface area is smaller and thus
  it cuts the fruit easily and smoothly.

5
Other applications

• Some other applications of pressure can be seen
  with the following examples

6
Pressure of solid on a solid

• For example, if you push on an object with your
  hand with a force of 20 pounds, and the area of
  your hand is 10 square inches, then the pressure
  you are exerting is 20 / 10 2 pounds per square
  inch.

7
Pressure of solid on a solid

• Pressure equals Force divided by Area
• You can see that for a given force, if the
  surface area is smaller, the pressure will be
  greater. If you use a larger area, you are
  spreading out the force, and the pressure (or
  force per unit area) becomes smaller.

8
Solid pressing on confined fluid

• When a liquid or gas is confined in a container
  or cylinder, you can create a pressure by
  applying a force with a solid piston. The
  pressure created in the cylinder equals the force
  applied divided by the area of the piston P
  F/A.

9
Solid pressing on confined fluid

• In a confined fluidthe pressure is equal
  throughout the container, pressing equally on all
  the surrounding walls. In the example of a
  bicycle pump, the pressure created inside the
  pump will be transmitted through the hose into
  the bicycle tire.
• Pressure is in all directions in a fluid
• Increasing the force will increase the
  pressure inside the cylinder.

10
Caused by gravity

• In special cases, since the weight of an object
  is a force caused by gravity, we can substitute
  weight in the pressure equation. Thus the
  pressure (P) caused by the weight (W) of an
  object is that weight divided by the area (A)
  where the weight is applied.
• P W/A

11
Caused by gravity

• If you place a solid object on the floor, the
  pressure on the floor over the area of contact is
  the weight of the object divided by the area on
  the floor.

12
Formula

• P is the pressure
• F is the normal force
• A is the area.
• PF/A or PdF/dA

13
Hydrostatic Pressure

• Hydrostatic pressure is the pressure exerted by a
  fluid at equilibrium due to the force of gravity
• It can be determined from a control volume
  analysis of an infinitesimally small cube of
  fluid

14
Hydrostatic Pressure

• Hydrostatic pressure can be calculated according
  to the following formula
• p is the hydrostatic pressure (Pa),
• ? is the fluid density (kg/m3),
• g is gravitational acceleration (m/s2),
• A is the test area (m2),
• z is the height (parallel to the direction of
  gravity) of the test area (m),
• z0 is the height of the zero reference point of
  the pressure (m).

15
Atmospheric pressure

• Statistical mechanics shows that, for a gas of
  constant temperature, T, its pressure, p will
  vary with height, h, as
• P(h)p(0)e-Mgh/kT
• where
• g  the acceleration due to gravity
• T  Absolute temperature (i.e. kelvins)
• k  Boltzmann constant
• M  mass of a single molecule of gas
• p  pressure
• h  height

16
Atmospheric pressure

• If there are multiple types of molecules in the
  gas, the partial pressure of each type will be
  given by this equation. Under most conditions,
  the distribution of each species of gas is
  independent of the other species.

17
Buoyancy

• Any body of arbitrary shape which is immersed,
  partly or fully, in a fluid will experience the
  action of a net force in the opposite direction
  of the local pressure gradient. If this pressure
  gradient arises from gravity, the net force is in
  the vertical direction opposite that of the
  gravitational force. 
• This vertical force is termed buoyancy or buoyant
  force and is equal in magnitude, but opposite in
  direction, to the weight of the displaced fluid.

18
Buoyancy

• In the case of a ship, for instance, its weight
  is balanced by a buoyant force from the displaced
  water, allowing it to float. If more cargo is
  loaded onto the ship, it would sink more into the
  water - displacing more water and thus receive a
  higher buoyant force to balance the increased
  weight.
• The person who discovered buoyancy is Archimedes.

19
Bibliography

• References
• http//en.wikipedia.org/wiki/PressureFormula
• http//en.wikipedia.org/wiki/Pressure
• http//en.wikipedia.org/wiki/Fluid_statics
• Pictures
• http//www.google.com.sg/pictures

20
Thank you!