Using the formula for pressure, making sure all values are in their standard unit: A 1.2 1.2 1.44 m2 p
F A 720
The pressure it exerts at the table is 500 Pa. 144 500
Pressure in Liquids and Gasses
Liquids and gasses are both classified as fluids, as both these states of matter can flow. It can be proven that pressure in a fluid is equal to the product of depth (h), density ( ) and acceleration due to gravity (g).3
r
PRESSURE IN FLUIDS r
r
BLAISE PASCAL, 1623–62 (FRENCH) He clarified the concepts of
pressure, studied vacuums and fluid mechanics. The SI unit of pressure is named in his honour.
p gh p pressure, density, g acceleration due to gravity, h depth
When investigating the difference in pressure in a column of fluid,we can assume that the density of the fluid and acceleration due to gravity do not change. Therefore the only variable affecting pressure is depth in the fluid.
At any given depth pressure is the same in all directions. Pressure acts perpendicularly to any surface that the fluid is placed in.
(a)
(b)
Fig 4.6: Pressure in liquids (a) varies with depth and also (b) acts perpendic- ularly to the surface of the container storing it
3Proof of this is on the website www.gillmacmillan.ie for illustrative purposes as it is not subject to examination.
