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Work and Machines

Work and Machines. Work: is the transfer of energy that occurs when a force makes an object move For work to be done, a force must make something move ex: pushing on something that doesn’t move is not doing work. Two conditions have to be met to do work on an object 1. object has to move

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Work and Machines

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  1. Work and Machines Work: is the transfer of energy that occurs when a force makes an object move For work to be done, a force must make something move ex: pushing on something that doesn’t move is not doing work

  2. Two conditions have to be met to do work on an object • 1. object has to move • 2. motion of the object must be in same direction as force applied When work is done, a transfer of energy always occurs So: Energy is also the ability to do work (not just the ability to cause change)

  3. Calculating Work • Work = force X distance • OR • W = F X d • *Units for work are Joules • (Practice Calculating Work)

  4. Using Machines • Machines: a device that makes doing work easier • Machines increase the force applied to an object OR increase the distance over which a force can be applied Machines can also change the direction of an applied force Ex: car jacks, ramps, wedges

  5. Effort and Resistance Forces • Two forces are involved when a machine is used to do work • Effort force: the force applied to the machine • Resistance force: the force applied by the machine to overcome resistance • Ex: when you pull a nail out w/a hammer, effort force is applied to the handle, resistance force is applied to the nail by the claw

  6. Efficiency: a measure of how much of the work put into a machine is changed into useful output work by the machine • High efficiency means less heat produced from friction • Efficiency = W output/W input X 100% • Friction causes output work to always be less than the input work • SO: Efficiency of a real machine is always less than 100%

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