# 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?
input
4. work done by the object is energy input/output?
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
 Author: Gymnastxoxo17 ID: 268976 Card Set: Work & Energy Updated: 2014-05-25 15:36:28 Tags: Chapter Five Folders: H Physics Description: , Show Answers: