Work

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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

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x
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x
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Work-Kinetic Energy Theorem

• The net work done on an object
• The kinetic energy of an object
• The Work-Kinetic Energy Theorem

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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.

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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)

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

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Conservation of Mechanical Energy

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

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Spring Potential Energy

• This is also called the Elastic Potential Energy.

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• 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.

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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

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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.

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