PRESSURE OF A FLUID air pressure height of

PRESSURE OF A FLUID air pressure = height of mercury column Barometer

Gauge pressure – pressure above the atmospheric pressure. absolute (total) pressure = gauge pressure + atmospheric press.

Pressure is produced by the weight of the fluid above the surface.

force weight of fluid pressure = -----------area mg density · volume · g = ---------------area density · (area · height) · g = ----------------area

pressure = density · height · g P = ρhg gauge pressure P = ρhg + P 0 absolute pressure SI units: 2 pressure: N/m = Pascals (Pa) 3 density: kg/m height (depth): m

Standard atmospheric pressure 760 mm Hg ≈ 30 in Hg Calculate 1 atm in Pascals P = ρgh 3 10 3 kg/m ρHg = 13. 6 x g = 9. 8 N/kg h = 0. 760 m 5 P = 1. 013 x 10 Pa

Pressure of fluid depends on depth.

Pressure does not depend on volume, only on height (depth). “Water seeks its own level”

More pressure at greater depth

Measure blood pressure at upper arm same height as heart

Pascal’s Principle – The pressure in an enclosed fluid is constant throughout the fluid. p 1 F 1 --A 1 = = p 2 F 2 --A 2

Pascal’s Principle When force is applied to a confined liquid, the change in pressure is transmitted equally to all parts of the fluid. Draw a bottle of water with arrows to illustrate the regular exerted pressure. Then draw a water bottle that you squeeze. What happens to the pressure? What happens if you open the top? How does Pascal’s Principle explain what

A force applied to one section of an enclosed liquid at rest will be transferred to the entire liquid with the same amount of force.

Hydraulic Systems A force applied to one piston increases the fluid pressure throughout the fluid. If the second piston has a larger surface area, the force is multiplied! Pressure = Force/Area = Pressure = Larger Force/Larger Area