Atmospheric Pressure & Gauge Pressure
At sea level
1.013 × 105 N/m2 = 1 atm = 101.3 kPa = 760 mm Hg = 760 torr
1 bar = 1.00 × 105 N/m2 = 100 kPa
GAUGE pressure – P measured over and above atmospheric pressure–sort of like using the tare button on a balance to remove the mass of a weighing container
Absolute P = P atm + P gauge
Pascal's Principle
Blaise Pascal (1623-1662) stated that: Pressure applied to a confined fluid increases the pressure throughout by the same amount.
Earth’s atmosphere exerts a pressure on ALL objects with which it is in contact, including other fluids & external P is transmitted through that fluid
The pressure due to water @ a depth of 100m below the surface of a lake is
ΔP = ρgΔh = (1,000 kg/m3)(9.8 m/s2)(100 m) = 9.8 × 105 N/m2 = 9.7 atm for just H2O!
Add the atmospheric pressure of the Earth’s atmosphere and the pressure is 10.7 atm (at sea level)
hydraulics –a small force can be used to exert a large F by making the area of one piston [the output] larger than the area of the other piston [the input]
Assume the input & output pistons are at the same h so Pascal’s principle applies
The quantity Fout/Fin is called the mechanical advantage and is equal to the
ratio of the areas.
IF the area of the output piston is 20 × that of the input
cylinder, the F is multiplied by 20; thus a force of 200 lbs could lift a 4,000
lb car!