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Chapter Nine: Simple Machines
9.1 Types of Simple Machines 9.2 Mechanical Advantage 9.3 Levers in the Human Body
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9.3 Levers in the human body
The human body is a complex machine that includes a number of simple machines—levers. Your arms and legs, for example, work as levers to move and lift objects.
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9.3 Levers in the human body
A classic example of a third class lever is a broom. A broom does not multiply force, but it does multiply speed. Since your limbs are third class levers, they multiply speed to do tasks quickly.
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9.3 Levers in the human body
Human arms and legs are examples of third class levers because the input forces are between a fulcrum and the output force. The output force is what you accomplish with your hands and feet. Where is the input force and the fulcrum?
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9.3 Levers in the human body
In the human body, all bones act as levers and each joint can serve as a fulcrum. When lifting your head, your neck works as a first-class lever. When you stand on your toes, the feet act as second-class levers. When biting, your jaw works as a third-class lever.
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