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Title:

Work

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Work The displacement of an object in a parallel direction to an applied force. F d W=Force x displacement W=Fd The force and displacement must be in parallel directions. – PowerPoint PPT presentation

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Title: Work


1
Work
  • The displacement of an object in a parallel
    direction to an applied force.

F
d
WForce x displacement
WFd
The force and displacement must be in parallel
directions.
Work is measured in Joules (J) which comes from a
Newton-meter (Nm).
The fundamental units that make up a Joule are
kgm2/s2
Work is a scalar quantity.
2
Vertical Work
hf
F
FW for a mass lifted at constant velocity
d
dchange in heightfinal height initial height
hi
Vertical Work Work(weight)(?h)
W
3
d
F
No work is accomplished by force F in this
situation.
4
Work
  • Also defined as a transfer of energy.
  • Whenever work is accomplished, energy of some
    type is transferred.

5
Work by various components
f
F
d
WFFd Work accomplished by force, F moving a
distance d Wf -fd Work accomplished by
friction through a distance, d.
Constant velocity Net work is zero WnetFnet(d)(F
-f)dFd-fdWF-Wf0
Acceleration WnetFnet(d)mad(F-f)dWF-Wf
6
Work is positive when the force and
displacement are in the same direction.
F
d
F
Work is negative when the force and displacement
are in opposite directions.
d
  • Positive work
  • Work is accomplished by the force.
  • Energy in transferred into the system
  • Negative work
  • Work is accomplished on the force.
  • Energy is transferred out of the system

7
  • Work is the area under a force-displacement graph.

8
Power
  • Power is the rate of doing work.
  • Power is the rate of energy transfer.
  • Power Work/time ? P W/t
  • Power (F)(d)/t F(d/t)
  • Power Force x velocity ? PFv
  • v average velocity (vfvi)/2
  • P ? (N)(m)/s (J)/(s)(kgm2/s3) Watt
  • Power is measured in Watts, abbreviated W.
  • 1 horsepower 746 Watts (1 hp 746 W)

9
Work in Various Directions
d
10
Situation 1
An object pulled at an angle on a level
horizontal surface.
F
The applied force F and d are not in a parallel
direction.
WFxd
Fx
FxFcos?
W(Fcos?)d
d
11
Situation 2
h
W
?
x
Given W, x, ?
hxtan?
WorkWhWxtan?
12
Situation 3
d
F
?
x
Given F, x, ?
dx/cos?
WFd
13
Situation 4
F
d
?
?
x
F
Given F, d, ?
xdcos?
or
F!!Fcos?
WFx WFdcos?
WFdFdcos?
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