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Chapter 5 ps

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simple machines, work, power

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Transcript of "Chapter 5 ps"

  1. 1. Chapter 5Chapter 5 Simple machinesSimple machines
  2. 2. WORKWORK  The transfer ofThe transfer of energy that occursenergy that occurs when a force makeswhen a force makes an object movean object move  In order forIn order for workwork toto be done a force mustbe done a force must make an objectmake an object movemove
  3. 3. 2 Conditions of work2 Conditions of work  1. The object1. The object must movemust move  2. Movement must be in the2. Movement must be in the same directionsame direction asas the force appliedthe force applied
  4. 4. Work and EnergyWork and Energy  When work is done there is always a transferWhen work is done there is always a transfer of energyof energy  Energy is the ability to do workEnergy is the ability to do work  When you do work on an object, you increaseWhen you do work on an object, you increase its energyits energy
  5. 5. Calculating workCalculating work  Work (J) = Force (N) x distance (m)Work (J) = Force (N) x distance (m)  W = FdW = Fd
  6. 6. PowerPower  The rate at which work is doneThe rate at which work is done  SI unit for power is theSI unit for power is the Watt (W)Watt (W)  P (watts) = Work (J)/Time (s)P (watts) = Work (J)/Time (s)  Usually expressed in kilowattsUsually expressed in kilowatts
  7. 7. Power and EnergyPower and Energy  Power is the rate at which energy is transferredPower is the rate at which energy is transferred  Power (w) = energy (J)/Time (s)Power (w) = energy (J)/Time (s)
  8. 8. MachineMachine  A device that makes doing work easierA device that makes doing work easier
  9. 9. Simple MachinesSimple Machines  A Machine that doesA Machine that does work with onlywork with only oneone movementmovement of theof the machinemachine  6 types6 types of simpleof simple machines: lever, pulley,machines: lever, pulley, wheel and axle, inclinedwheel and axle, inclined plane, screw, and wedgeplane, screw, and wedge
  10. 10. LeverLever  A bar that is freeA bar that is free to pivot or turnto pivot or turn around a fixedaround a fixed pointpoint  The fixed point isThe fixed point is called a fulcrumcalled a fulcrum  There are 3There are 3 classes of leversclasses of levers
  11. 11. PulleyPulley  A grooved wheel with aA grooved wheel with a rope, chain, or cablerope, chain, or cable running along therunning along the groovegroove  The axle of the pulleyThe axle of the pulley acts as the fulcrumacts as the fulcrum  Fixed and movableFixed and movable  Fixed IMA = 1,Fixed IMA = 1, Movable IMA = 2Movable IMA = 2
  12. 12. Block and Tackle pulleyBlock and Tackle pulley  A system of pulleysA system of pulleys consisting of bothconsisting of both fixedfixed and movableand movable pulleyspulleys  IMA is equal to theIMA is equal to the number of ropenumber of rope segmentssegments that supportthat support the weightthe weight
  13. 13. Wheel and AxleWheel and Axle  consists of a shaft orconsists of a shaft or axle attached to a largeraxle attached to a larger wheel.wheel.  The wheel and axleThe wheel and axle rotate togetherrotate together  Examples:Examples: PencilPencil sharpeners, door knobs,sharpeners, door knobs, screw drivers, faucetscrew drivers, faucet handleshandles
  14. 14. Inclined PlaneInclined Plane  A sloping surface, suchA sloping surface, such as a ramp.as a ramp.  Reduces the amount ofReduces the amount of force required to doforce required to do workwork  IMA = Length of slopeIMA = Length of slope (m)/Height (m)(m)/Height (m)
  15. 15. ScrewScrew  An inclined planeAn inclined plane wrapped in a spiralwrapped in a spiral around a cylindricalaround a cylindrical postpost  IMA is related to theIMA is related to the spacing of the threadsspacing of the threads
  16. 16. WedgeWedge  AnAn inclined planeinclined plane withwith one or two sloping sidesone or two sloping sides  ItIt changes the directionchanges the direction of theof the input forcesinput forces
  17. 17. Compound MachineCompound Machine  Two or moreTwo or more simple machines that operatesimple machines that operate togethertogether  A car is a compound machineA car is a compound machine
  18. 18. Compound MachinesCompound Machines
  19. 19. 2-Forces Involved in Work2-Forces Involved in Work 11.. Input Force:Input Force: The force that is applied to theThe force that is applied to the machine. (effort force)machine. (effort force) Given the symbolGiven the symbol FFinin 2.2. Output Force:Output Force: The force applied by theThe force applied by the machine.machine. Given the symbolGiven the symbol FFoutout
  20. 20. 2-Types of Work done on a Machine2-Types of Work done on a Machine 1.1. Input Work:Input Work: The work done by you on theThe work done by you on the machine.machine. Given the symbolGiven the symbol WWinin 2.2. Output Work:Output Work: The work done by theThe work done by the machine.machine. Given the symbolGiven the symbol WWoutout
  21. 21. Conserving EnergyConserving Energy  A machineA machine cannotcannot create energy, so…create energy, so… WWoutout cancan never benever be greater thangreater than WWinin
  22. 22. Which means that…Which means that…  WWoutout will always bewill always be lessless thatthat WWinin ……  because friction changes some of the energybecause friction changes some of the energy to heat.to heat.
  23. 23. Ideal MachineIdeal Machine  A machine without friction.A machine without friction.  WWinin = W= Woutout
  24. 24. Mechanical AdvantageMechanical Advantage  The ratio of the output force to the input force.The ratio of the output force to the input force.  Can be calculated using the following equation.Can be calculated using the following equation.
  25. 25. EfficiencyEfficiency  A measure of how much of the input work put into aA measure of how much of the input work put into a machine is change into useful output.machine is change into useful output.
  26. 26. Efficiency Cont…Efficiency Cont… • The efficiency of an ideal machine is 100 percent. • The efficiency of a real machine is always less than 100 percent.
  27. 27. How can machines be made moreHow can machines be made more efficient???efficient??? • by adding a lubricant, such as oil or grease, to surfaces that rub together.
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