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Work and Machines. Machines Do Work. A Machine is a device that changes a force. Ex. A Jack used to change a tire. Machines make work easier to do. They change the size of a force needed The direction of a force The distance over which a force acts. Machines Do Work.

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Machines do work
Machines Do Work

  • A Machine is a device that changes a force.

    • Ex. A Jack used to change a tire.

    • Machines make work easier to do.

      • They change the size of a force needed

      • The direction of a force

      • The distance over which a force acts


Machines do work1
Machines Do Work

  • The more Force applied, the shorter the overall distance.

    • Ex. Carry 5 books at the same time from Mrs. Larose's class to Mrs. Hendee’s class.

  • The less force applied, the longer the overall distance.

    • Ex. Carry one book at a time from Mrs. Larose's class to Mrs. Hendee’s class


Machines do work2
Machines Do Work

  • Change in direction of applied force.

    • Ex. Pulling back on the handle of a oar causes its other end to move in opposite direction.

    • If the oar is pushed father away from the boat, how will the force needed to pull the oar through the water change?


Work input and work output
Work Input and Work Output

  • A rower pulls back on each oar handle and the other end of the oar pushes against the water.

  • Work is done on the oar (Machine) by pulling on them, and the oars do work on the water to move the boat.

  • Because of friction, the work done by a machine is always less than the work done on the machine


Work input and work output1
Work Input and Work Output

  • The force you exert on a machine is called input force.

  • The distance the input force acts through is called input distance.

  • The work done by the input force acting through the input distance is called work input.

  • Formula:

    • Work input= Input force x input distance


Work output of a machine
Work output of a Machine

  • The force that is exerted by a machine is called output force.

  • The distance the output force is exerted through is called output distance.

  • Formula:

    • Work output= output force x output distance


Work output of a machine1
Work Output of a Machine

  • If there is no change in work input, there cannot be an increase in the work output.

  • You cannot get more work out of a machine than you put into it!


Mechanical advantage
Mechanical Advantage

  • The mechanical advantage of a machine is the number of times that the machine increases an input force.

  • The relation of input force used to operate a machine and the output force exerted by the machine depends on the type of machine and how it is used.

    • Ex. A nutcracker


Actual mechanical advantage
Actual Mechanical Advantage

  • The mechanical advantage determined by measuring the actual forces acting on a machine is the actual mechanical advantage

  • Formula:

    • Actual mechanical advantage= Output force

      Input force

      Ex. Long incline ramp


Ideal mechanical advantage
Ideal Mechanical Advantage

  • The ideal mechanical advantage of a machine is the mechanical advantage in the absence of friction.

  • Because friction is always present, the actual mechanical advantage of a machine is always less than the ideal mechanical advantage.

  • Formula:

    • Ideal mechanical advantage= Input distance

      Output distance


Calculating ima
Calculating IMA

  • A woman drives her car up onto wheel ramps to perform some repairs. If she drives a distance of 1.8 meters along the ramp to raise the car 0.3 meter, what is the ideal mechanical advantage of the wheel ramp?


Efficiency
Efficiency

  • The percentage of the work input that becomes work output is the efficiency of a machine.

  • Because there is always friction, the efficiency of any machine is always less than 100%.

  • The work output of a machine is always less than the work input.

  • Formula:

    • Efficiency= (Work input / Work output) x 100%


Calculating efficiency
Calculating Efficiency

  • You have just designed a machine that uses 1000J of work from a motor for every 800J of useful work the machine supplies. What is the efficiency of your machine?


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