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Unit 5 Work, Power, and Energy

Unit 5 Work, Power, and Energy. Chapters 10-11. Work. What is work? Physics definition: Work is the transfer of energy by mechanical means In order for work to be done the object must move W= Fd. energy. Energy is the ability to do work There are two types of energy Kinetic Potential

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Unit 5 Work, Power, and Energy

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  1. Unit 5Work, Power, and Energy Chapters 10-11

  2. Work • What is work? • Physics definition: Work is the transfer of energy by mechanical means • In order for work to be done the object must move W=Fd

  3. energy • Energy is the ability to do work • There are two types of energy • Kinetic • Potential • Energy is measured in Joules, represented by the symbol “J” • Kinetic Energy is the energy that a moving object posesses • KE =1/2mv2

  4. Work-Energy Theorem • How can we connect work and energy mathematically? • Work-energy theorem: when work is done on an object, the result is a change in kinetic energy W=ΔKE

  5. Work • Work done at an angle can be calculated with the equation W=Fdcosθ • Work can also be calculated by finding the area under the curve of a force-displacement graph • If several forces are exerted on a system, calculate the work done by each force and then add the results

  6. Power • Power is the rate of doing work, that is the rate at which energy is being transferred P=W/t • Power is measured in watts, represented by the symbol “W” • One watt is 1J of energy transferred in 1 second

  7. James Joules • Newtons times seconds • N ● s • James Watts- W • Joules per second • J / s

  8. James Watts

  9. Machines • What is a machine? • A machine eases the load by changing either the magnitude or the direction of a force to match the force to the capability of the machine or the person • Machines do not change the amount of work done but rather make the task easier

  10. Types of Machines • Most machines, no matter how complex, are combinations of one or more of the six simple machines • Lever • Pulley • Wheel and axel • Inclined plane • Wedge • Screw

  11. Compound Machines • Compound machine- a machine consisting of two or more simple machines linked in such a way that the resistance force of one machine becomes the effort force of the second • The mechanical advantage of a compound machine is found by multiplying the MA of each of the simple machines • MA=MAmachine 1 x MAmachine 2

  12. Mechanical Advnatage • The mechanical advantage, MA, is the ratio of resistance force to effort force • MA =Fr/Fe • The ideal mechanical advantage of a machine, IMA, is the ratio of the distances moved • IMA= de/dr • In all real machines, MA is less than IMA

  13. Efficiency • In a real machine, not all of the input work is available as output work. Consequently the machine is less efficient at accomplishing the task • The efficiency of a machine is defined as the ratio of output work to input work e = (Wo/Wi)100 • The efficiency of a machine can be found from the real and ideal mechanical advantages e = (MA/IMA)100

  14. Classwork/Homework • Practice Problems • Pg261-264 • #1-14

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