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=

  F   A

  p=pressure (Pa) or (N/m²)

  F=force (N) 

  A=area (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.