Unit 1 General physics
Section 1.8 Pressure
- Pressure is defined as the force per unit area.
- Pressure has the symbol p and its unit is the pascal (Pa).
Pressure, force and area are related by the formula:
p=pressure (Pa) or (N/m2)
- 1Pa is equivalent to 1N/m2 (newton per metre squared).
- Pressure can be increased by increasing the force on a constant area.
- Pressure can be increased by decreasing the area for a constant force.
A girl weighing 500N and wearing high heels with an area of 2cm2 in contact with the floor can make indentations on a wooden floor, because the pressure she exerts is 2500000Pa.
An elephant weighing 40000N and standing on all four feet, a total area of 0.4m2, would exert a pressure of only 100000Pa.
- A sharp knife cuts bread more easily than a blunt knife. This is because the sharp knife has a much smaller surface area in contact with the bread than a blunt knife. When you push down on the knife (exert a force) the sharp knife exerts greater pressure on the bread and it cuts easily.