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 

     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.
 
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