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C1.13 Levers

Text 15 pg 230

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Lever Systems

  • Every moveable bone in the human body is part of a lever system that facilitates movement
  • Three classes of levers
    • Class I lever (e.g. teeter-totter)
    • Class II lever (e.g. wheelbarrow)
    • Class III lever (e.g. snow shovelling)

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  • Simple machines that augment the amount of work done by an applied force

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Lever Systems

LEVERS:

  • A lever is a rigid structure (ie limb) hinged at one point and to which forces are applied at two other points.

• The hinge or pivot point is called the fulcrum (▲)

•One of the forces is called the weight or resistance that opposes movement (R) usually gravity

•The third point is called the force that causes or intends to cause movement of the lever. (F)

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Lever Systems

  • Class I lever (e.g. teeter-totter)
    • The fulcrum (axis) is located between the force (effort) and the resistance load

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Lever Systems

  • Class II lever (e.g. wheelbarrow)
    • The resistance is between the force and the fulcrum
    • least common in the body

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© iStockphoto.com/”GeofferyHolman”

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Lever Systems

  • Class III lever (e.g. shovelling)
    • The force is between the fulcrum and the resistance
    • most common type in the body

© iStockphoto.com/”tacojim”