Lecture 16: Angular momentum

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Lecture 16Angular momentum

• Phys 2101
• Gabriela González

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Example

• A constant horizontal force of magnitude 10 N is
  applied to a wheel of mass 10 kg and radius 0.30
  m as shown in the figure. The wheel rolls
  smoothly on the horizontal surface, and the
  acceleration of its center of mass has magnitude
  0.60 m/s2. (a) What are the magnitude and
  direction of the frictional force on the wheel?
  (b) What is the rotational inertia of the wheel
  about the rotation axis through its center of
  mass?

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Torque

• Our definition for torque produced by a given
  force F about a point P as
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  t F r sinq
• allows us to add up torques only when the forces
  are all in the same plane.

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Angular momentum

• The angular momentum of a particle with respect
  to a point is defined as

The angular momentum of a system of particles is
the sum of the angular momenta of each particle.
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Newtons second law (again!!)

• For a single particle, Fma can also be written
  as

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Newtons law systems of particles
total linear momentum
total angular momentum
No forces, no linear momentum conservation of
linear momentum. No torques, no angular momentum
conservation of angular momentum.
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Newtons law