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5.2 Using Machines.

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Presentation on theme: "5.2 Using Machines."— Presentation transcript:

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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