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# 14 2 Work And Machines

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### 14 2 Work And Machines

1. 1. 14.2 Work and Machines How Do Machines Make Work Easier? How Are Work Input and Work Output Related for a Machine?
2. 2. Machines Do Work <ul><li>Machines = are devices that change force </li></ul><ul><li>Ex. Car Jack, Lug wrench,Car </li></ul><ul><li>Machines make work easier </li></ul>
3. 3. Machines Do Work <ul><li>Machines change the size of force needed </li></ul><ul><li>Machines change the direction of a force </li></ul><ul><li>Machines change the distance over which a force acts </li></ul>
4. 4. Work Input and Work Output <ul><li>Input Force- is the force you exert on a machine. </li></ul><ul><li>Input Distance- the distance the input force acts through. </li></ul><ul><li>Work Input- work done by the input force acting through the input distance. </li></ul>
5. 5. Work Input and Work Output <ul><li>Equation: </li></ul><ul><li>Work input = the input force X input distance . </li></ul><ul><li>Equation: </li></ul><ul><li>Work Output = the output force X output distance. </li></ul>
6. 6. Work Input & Work Output <ul><li>Output Force- the force exerted by a machine. </li></ul><ul><li>Output distance- the distance the force is exerted through. </li></ul>
7. 7. 14.3 Mechanical Advantage and Efficiency How Does the Actual Mechanical Advantage of a Machine Compare to Its Ideal Mechanical Advantage? Why Is the Efficiency of a Machine Always Less Than 100%?
8. 8. Mechanical Advantage <ul><li>Mechanical Advantage of a machine is the number of times a machine increases an input force </li></ul>
9. 9. Actual Mechanical Advantage <ul><li>Mechanical Advantage that is measured </li></ul><ul><li>Actual Mechanical Advantage = </li></ul><ul><li>Output Force / Input Force </li></ul>
10. 10. Ideal Mechanical Advantage <ul><li>Mechanical advantage in the absence of Friction </li></ul><ul><li>Calculation depends on location of forces and distances over which they act </li></ul><ul><li>Ideal Mechanical Advantage = </li></ul><ul><li>Input distance / Output distance </li></ul>
11. 11. Efficiency <ul><li>Is the percentage of work input that becomes work output. </li></ul><ul><li>Efficiency = </li></ul><ul><li>Work output / Work input X 100%. </li></ul><ul><li>Friction makes the efficiency less than 100%. </li></ul>