pgs. 317 - 342

Calculate the pressure exerted by a fluid. Explain Pascal’s Principle. Calculate how pressure varies with depth in

a fluid.

A measure of the force applied to a surface per unit area

SI unit of pressure is the Pascal (Pa) = 1 N/m2

The pascal is a small amount of pressure

At sea level, the pressure of the atmosphere is 1.01x 105 Pa

This amount of air pressure is the basis for another unit, atmosphere

1 atm = 1.01 x 105 Pa

Atmospheric pressure is normally about 100,000 Pascals.

Differences in atmospheric pressure cause winds to blow.

Low atmospheric pressure inside a hurricane’s eye contributes to the severewinds and the development of the storm surge.

The force on a surface caused by pressure is always normal (or perpendicular) to the surface. This means that the pressure of a fluid is exerted in all directions, and isperpendicular to the surface at every location.

Calculate the net force on an airplane window if the cabin pressure is 90% of the pressure at sea level and the external pressure is only 50% of that at sea level. The window is 0.43m tall and 0.30m wide.

Applied pressure is transmitted equally throughout a fluid

The small piston of a hydraulic lift has an area of 0.20 m2. A car weighing 1.20 x 104 N sits on a rack mounted on the large piston. The large piston has an area of 0.90 m2. How large a force must be applied to the small piston to support the car?

P = ρghP: pressure (Pa)ρ : density (kg/m3)g: acceleration constant (9.81 m/s2)h: height of liquid column (m)

This type of pressure is often called gauge pressure. Why?

If the liquid is water, this is referred to as hydrostatic pressure.

Absolute pressure is obtained by addingthe atmospheric pressure to the hydrostatic pressure.

Pressure varies with the depth of a fluid

Po = 1.01 x 105 Pa

Buoyant forces arise from the differences in fluid pressure between the top and bottom of an immersed object.

Pnet = Pbottom - Ptop

Atmospheric pressure is pressure from above

The weight of the air in the upper portion of Earth’s atmosphere exerts pressure on the layers below

Mercury barometer is commonly used to measure atmospheric pressure

Calculate the absolute pressure at an ocean depth of 1.00 x 103 m. Assume that the density of the water is 1.025 x 103 kg/m3 and that P0 = 1.01 x 105 Pa.