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12.2

12.2. How Machines Do Work?. What Is A Machine?. Name some machines A machine is a device that allows you to do work in a way that is easier or more effective

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12.2

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  1. 12.2 How Machines Do Work?

  2. What Is A Machine? • Name some machines • A machine is a device that allows you to do work in a way that is easier or more effective • A machine makes work easier by changing at least 1 of 3 factors: the amount of force you exert, the distance over which you exert your force, or the direction in which you exert your force • The force you exert on the machine is the input force, which moves the machine a certain distance called an input distance • The force exerted by the machine over another distance is the output distance • The force the machine exerts on an object is the output force

  3. The input force that we exert on the machine and the distance the machine moves is called the input work • The output force and distance exerted by the machine is the output work • When using machines, the amount of input work is equal to the amount of output work

  4. Changing Force • In some machines, the output force is greater than the input force • If a machine allows you to use less input force to do the same amount of work, you must apply that input force over a greater distance

  5. Changing Distance • In some machines, the output force is less than the input force • Why would you want a machine that allows you to exert your input force over a shorter distance? • In order for this machine to work, you have to apply a greater input force

  6. Changing Direction • Some machines don’t change either force or distance • What could be the advantage to a machine that doesn’t change force or distance?

  7. Mechanical Advantage • A machine’s mechanical advantage is the number of times a machine increases a force exerted on it • The mechanical advantage can be found by dividing the output force by the input force • When the output force is greater than the input force, the mechanical advantage of the machine is greater than 1 (hand-held can opener) • For a machine that increases the distance, the output force is less than the input force, which makes the mechanical advantage less than 1 (ramp) • If direction is the only thing to change, the input a1nd output force will be equal and the mechanical advantage will always be 1

  8. Efficiency of Machines • In every machine, some work is wasted overcoming the force of friction • The less friction there is, the closer the output work is to the input work • Efficiency of a machine compares the output work to the input work and is expressed as a percent (%) • The higher the percentage, the more efficient the machine • Efficiency can be calculated if you know the input and output work for a machine (2 factors)

  9. Efficiency=output work/input work x 100% • An ideal machine would be one with an efficiency of 100%, but they do not exist • in all machines, some work will be wasted due to friction • All machines will have an efficiency of less than 100% • A machine’s measured mechanical advantage is called actual mechanical advantage

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