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5.2

5.2. Using Machines. What is a Machine?. Machine : device that makes doing work easier. Knife Scissor Doorknob Car engine. Making work easier. Machines make work easier by: increasing the force that can be applied to an object. Car Jack allows you to lift car

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5.2

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  1. 5.2 • Using Machines

  2. What is a Machine? • Machine: device that makes doing work easier. • Knife • Scissor • Doorknob • Car engine

  3. Making work easier • Machines make work easier by: • increasing the force that can be applied to an object. • Car Jack allows you to lift car • Increasing the distance over which a force can be applied. • Ramps • Changing the direction of an applied force. • Pull down on cord for blinds • Amount of work does not change

  4. Work done by Machines • Crowbar – when you do work on the machine (crowbar), it does work on the lid. • 2 Forces involved: • Effort force: force applied to the machine • Resistance force: force applied by the machine • 2 types of Work: • Input work: Work done by you on a machine • Output work: Work done by the machine

  5. Conserving Energy • When you do work on a machine, you transfer energy to the machine. • The work you get out of a machine can never be more than what you put into the machine. • Actually some energy is always lost to friction so W(out) is always less than W(in).

  6. Ideal Machines • W(in) = W(out) • Fe X de = Fr X dr • Fe = Force effort (what you exert) • Fr = Force resistance (what you are moving) • De = Distance effort • Dr = Distance resistance • Hammer example

  7. Mechanical Advantage • The number of times a machine multiplies the effort force. • MA = Fr Fe * When only the direction of force changes, the MA = 1

  8. Efficiency • A measure of how much of the work you put into a machine is changed to useful output work by the machine. • Eff = Wout X100% Win Efficiency is always less than 100% **Increase efficiency by decreasing friction.

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