## Unit 1 General physics

Notes

## 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= F

Ap=pressure (Pa) or (N/m

^{2})F=force (N)

^{ }A=area (m

^{2})- 1Pa is equivalent to 1N/m
^{2}(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 2cm

^{2}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 0.4m

^{2}, 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.