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Work

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... vs. Nonconservative forces ... is a nonconservative force. Gravitational Potential ... a system with no nonconservative forces, the total mechanical ... – PowerPoint PPT presentation

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Title: Work


1
Work
  • The work done on an object by a constant force is
    given by
  • Units Joule (J)
  • The net work done on an object is the sum of all
    the individual works

2
x
3
x
4
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5
Work-Kinetic Energy Theorem
  • The net work done on an object
  • The kinetic energy of an object
  • The Work-Kinetic Energy Theorem

6
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8
Conservative vs. Nonconservative forces
  • There are two general kinds of forces
    conservative forces and nonconservative forces.
  • A force is conservative if the work it does in
    moving an object between two points is the same
    no matter which path is taken.
  • Gravity is a conservative force.
  • Friction is a nonconservative force.

9
Gravitational Potential Energy
  • The gravitational potential energy of a system
    consisting of the Earth and an object of mass m
    near the Earths surface is given by
  • Units Joule (J)

10
  • What if there are no nonconservative forces (i.e.
    there is no friction)? Then Wnc0.

11
Conservation of Mechanical Energy
  • In a system with no nonconservative forces, the
    total mechanical energy of the system remains the
    same at all times.

12
Spring Potential Energy
  • This is also called the Elastic Potential Energy.

13
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15
  • The spring force varies it depends on x. So to
    figure out the work done by the spring force, we
    will use the average spring force.

16
Power
  • If an external force is applied to an object and
    if the work done by this force is W in the time
    interval Dt, then the average power is

17
Work done by a varying force
  • The work done by a variable force acting on an
    object that undergoes a displacement is equal to
    the area under the graph of F versus x.

18
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