#5.5.1.1
Pressure in a fluid 1
A fluid can be either a liquid or a gas.
The pressure in fluids causes a force normal (at right angles) to any surface.
The pressure at the surface of a fluid can be calculated using the equation:
\(\text{pressure} = \dfrac{\text{force normal to a surface}}{\text{area of that surface}}\)
\(p = \dfrac{F}{A}\)
pressure, p, in pascals, Pa
force, F, in newtons, N
area, A, in metres squared, m2
#5.5.1.2
Pressure in a fluid 2
The pressure due to a column of liquid can be calculated using the equation:
\(\text{pressure} = \text{height} × \text{density} × \text{gravitational field strength} \)
\( p = h ρ g \)
pressure, p, in pascals, Pa
height of the column, h, in metres, m
density, ρ, in kilograms per metre cubed, kg/m3
gravitational field strength, g, in newtons per kilogram, N/kg (In any calculation the value of the gravitational field strength (g) will be given.)
Students should be able to explain why, in a liquid, pressure at a point increases with the height of the column of liquid above that point and with the density of the liquid.
Students should be able to calculate the differences in pressure at different depths in a liquid.
A partially (or totally) submerged object experiences a greater pressure on the bottom surface than on the top surface. This creates a resultant force upwards. This force is called the upthrust.
Students should be able to describe the factors which influence floating and sinking.