Pgs.%20167-192

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Chapter 5 Pgs. 167-192
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• Recognize the difference
• between the scientific and
• layman definitions of work.
• Define work by relating it
• to force and displacement.

1. Identify where work is being performed in a
   variety of situations.
2. Calculate the net work done when many forces are
   applied to an object.

3
Work
Work tells us how much a force or combination of
forces changes the energy of a system. Work is
the bridge between force (a vector) and energy
(a scalar).
4
Work (W)

• Work is done on an object when a force is applied
  and the object moves
• W Fd
• Unit for work kgm2/s2 or Joule (J)
• SI System Joule (N m)
• 1 Joule of work is done when 1 N acts on a body
  moving it a distance of 1 meter

5

• Work is done only when the components of a force
  are parallel to a displacement
• There is no work done by a force if it does not
  cause displacement
• W Fd(cosT)
• Wnet Fnetd(cosT)

6

• Work is a scalar quantity
• Can be positive or negative
• Positive if your applied force and direction of
  movement are the same
• Ex. Pushing a vacuum
• Pulling a wagon

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• Negative if your applied force is opposite of the
  direction of movement
• Ex. Pushing against a remote control car that is
  going forward
• Pulling against a remote control car
  that is going in the opposite direction
• Friction does negative work on an object

8
Force Types

• Conservative forces related to potential energy
  changes and is path independent
• Non-conservative forces not related to
  potential energy changes and is path dependent

9

• How much work is done on a vacuum cleaner pulled
  3.0 m by a force of 50.0 N at an angle of 30.0
  above the horizontal?