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The Human Body

The Human Body. Chapter Nineteen: Support and Movement. 19.1 Bones and Muscles 19.2 The Human Body as a Machine. Investigation 19B. Levers and the Human Body. What types of levers does your body have?. 19.2 Forces.

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The Human Body

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  1. The Human Body

  2. Chapter Nineteen: Support and Movement • 19.1 Bones and Muscles • 19.2 The Human Body as a Machine

  3. Investigation 19B Levers and the Human Body • What types of levers does your body have?

  4. 19.2 Forces • A forceis a push or pull, or any action that has the ability to change motion. • Weight is a measure of the force exerted by gravity. • The newton (N) is the SI unit of force.

  5. 19.2 Forces • The newton is a smaller unit of force than the pound. • One pound of force equals 4.448 newtons.

  6. A simple machineis an unpowered mechanical device, such as a lever. Some other simple machines are a wheel and axle, ropes and pulleys, gears, and a ramp. 19.2 Simple Machines

  7. 19.2 Input and output • With a lever, the input force(also called the effort) is the force you apply. • The output forceis the force exerted on the load you are lifting. Output Input

  8. One person can easily lift an elephant with a properly designed system of ropes and pulleys! 19.2 Simple Machines

  9. 19.2 Mechanical advantage • The ability of a lever to perform a task depends on its mechanical advantage. • Mechanical advantageis the ratio of output force produced by a simple machine to the applied input force.

  10. 19.2 Mechanical Advantage • The input force that is applied to a lever and the output force are related to the lengths of the input and output arms.

  11. 19.2 Mechanical Advantage • A broom is a lever used to sweep floors. • A broom has a mechanical advantage of less than 1.

  12. 19.2 The three classes of levers • There are three types of levers: • First class levers • Second class levers • Third class levers • They are classified by the locations of the input and output forces relative to the fulcrum.

  13. 19.2 Levers in the human body • In the human body, all bones act as levers and each joint can serve as a fulcrum. • When biting, your jaw works as a third-class lever. • Your forearms work as third-class levers. • When you stand on your toes, the feet act as second-class levers.

  14. Technology Connection Prosthetic Legs and Technology • The human leg is a complex and versatile machine. • Designing a prosthetic (artificial) device to match the leg’s capabilities is a serious challenge.

  15. Activity Leg Levers: Digger or Runner • Some animals do a lot of running, while others spend a lot of their time digging. • In this activity you will find the mechanical advantage of bones to determine who is a digger and who is a runner.

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