Work & Energy

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  1. work
    • amount of mechanical energy transferred by a force acting through a distance
    • if a force does work, it must move the object, and the force has to be parallel to the displacement
  2. net work calculation
    net force x displacement x cosine of angle between them (with the horizontal)
  3. work done on the object is energy input/output?
  4. work done by the object is energy input/output?
  5. positive work
    • force makes the object go in the direction it traveled
    • like lifting a box up
  6. negative work
    • forces oppose the motion
    • like kinetic friction and displacement
  7. zero work
    force acts perpendicular to the motion
  8. energy
    capacity of a physical system to do work
  9. mass and energy relationship
    mass is another form of energy
  10. mechanical energy
    kinetic energy and all forms of potential energy
  11. conservative forces
    work done by these is stored as energy that can be released at a later time
  12. non-conservative forces
    work done by these cannot be recovered later as kinetic energy because it is instead converted to other forms
  13. conservation of mechanical energy
    mechanical energy is conserved in systems involving only conservative forces
  14. law of conservation of energy
    • within an isolated system, the amount of energy remains constant (energy cannot be created nor destroyed)
    • energy can only transfer from form to form, and the amount of energy you start with has to equal the amount of energy you end with
  15. isolated systems
    no external forces cause a change in the energy inside the system (you omit/don't consider some forces maybe; this is hypothetical usually)
  16. energy lost
    if work was done against non-conservative forces (like friction), then energy was lost by the system in doing work
  17. what does positive work mean for the speed
    speeds up; net force does work on the object
  18. what does negative work mean for the speed
    slows down; work done by the object on another object
  19. kinetic energy
    • the energy of an object due to its motion; increases with increases in mass and speed; present in moving objects
    • is like the work an object can do as it comes to rest, or the amount of energy stored in the object
  20. work kinetic energy theorem
    the net work equals the change in kinetic energy
  21. potential energy
    stored energy; energy associated with an object due to its position
  22. gravitational potential energy
    potential energy associated with an object due to the position of the object relative to the earth; depends on height of the object and free fall acceleration
  23. zero level
    vertical coordinate where the gravitational potential energy is zero
  24. elastic potential energy
    potential energy in a stretched or compressed elastic object; stored in any compressed/stretched object
  25. spring constant k
    • parameter that expresses how resistant a spring is to being compressed or stretched
    • small for flexible springs; large for stiff ones
  26. work energy theorem
    if work is done on or by an object, then we can expect there would be some change in the energy
  27. average power
    average rate at which work is done; rate of change of energy or energy transfer
  28. power units
    j/sec or watts
  29. what is meant by machines with different power ratings
    they do the same work in different time intervals

Card Set Information

Work & Energy
2014-05-25 15:36:28
Chapter Five
H Physics
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