# What is pressure

What is pressure? Pressure is the force acting normally per unit area of the surface.

A pascal is the pressure exerted when a force of 1N acts normally on an area of 𝟏 𝐦𝟐.

### Pressure in solids

Pressure in solids depends on;
Magnitude of force applied
Cross sectional area in contact

Maximum and Minimum Pressure
Pressure increases when the area decreases and decreases when the area increases.

Example 1:

The box below weighs 60N. Determine the maximum and minimum pressures it exerts on the ground.

Example 2:

A box of dimensions 20cm by 1m by10cm weighs 30kg. Determine the maximum and minimum pressures exerted by the box on the ground.

Given: -Dimensions; cm x 10cm x 20cm
-Mass, m = 30kg
-Acceleration due to gravity, g = 10ms-2

Example 3:

The dimension of a cuboid are 5cm x 10cm x 20cm and the mass of the cuboid is 6kg. Calculate the maximum and minimum pressures the cuboid exerts on the ground.

Solution
Given: – Dimensions; 5cm x 10cm x 20cm
-Mass, m = 6kg
-Acceleration due to gravity, g = 10ms-2

Example 4:

The tank below has a mass of 2.5kg. Determine the minimum and maximum pressure exerted by the tank on the ground; When it is;
(i) empty
(ii) filled with water up to the brim.
(iii) half filled with water. (Density of water =1000kgm-3)

Solution

Note: when calculating pressure, the unit of area of base should always be in m2. From the above calculations it is noted that: the greater the area over which the force acts normally the less is the pressure.

A tractor with wide wheels can pass over soft ground because the greater area of wide wheel exerts less pressure.

A hippopotamus of wide feet is able to walk on soft grounds without sinking because the greater area of wide hooves exerts less pressure.

When the same force is applied on a needle and nails both placed on the hand, one tends to feel more pain from the needle because the small area of needle exerts greater pressure.

A sharp knife cuts well than a blunt one.