Topic 7: Fluid Pressure
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The force acting perpendicular to a certain
surface area
continuous physical force exerted on or
against an object by something in contact
with it.
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Pressure (P)= Force (F)
Area (a)
Force(F) is measured in Newton's (N)
Area (a) is measured in square meters (m2)
Pressure (P) is measured in (N/m2)
◦ This is also called a Pascal (Pa)
◦ 1000 Pa = 1 kilopascal (kPa)
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When gases are compressed, they exert a
force back
We can use this property in vehicle shocks
◦ Vehicle shocks
◦ Car tires (the tubes)
◦ Air bags
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Earth’s atmosphere is approx. 160 km thick
Gravity keeps the envelope of air around
Earth
Just as water pressure changes with depth, air
pressure changes with altitude
◦ The higher the altitude, the less air particles
pressing against your body
◦ https://www.youtube.com/watch?v=QeAp3CuGjk8
◦ https://www.youtube.com/watch?v=7_yf-iRf8Vc
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Barometer
◦ Early barometer’s were made with Mercury
 Still used in many weather station’s today
◦ They are made from a thin glass tube that is sealed
at one end and open at the other and completely
filled with mercury
◦ The tube is then inverted (turned upside down) in a
pool of mercury
 This allows no air to enter the system
 Mercury falls to the lower level due to gravity
 Leaves a vacuum at the top
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As air pushes down on the mercury in the pol
which in turn pushes the mercury up the tube
until it equalizes with the pressure of gravity
Air pressure is 760 mm/Hg at sea level
https://www.youtube.com/watch?v=VqKkAJd
arZ8
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If in a closed container, the air pressure is
lower inside then on the outside the container
will buckle
◦ The pressures do not balance therefore creating an
unbalanced force
◦ Ex. Juice box