Summary

• Moment of inertia
• Torque & Newton's Second Law
• Static equilibrium

• Reading Quiz



• Angular momentum
  • L = Iω
    Example #1
    
  • Newton's second law
  • conservation of L
    Example #2
    
  • demos and applet
  
  
• Rotational work and power



• Interactive Example 11-7
• Active Example 11-5

Walker4e
Reading quiz When does an object moving in a straight line at constant speed have a nonzero angular momentum?
A. always
B. sometimes
C. never
Answer















gc6 8.52
What is the angular momentum of a 2.8 kg uniform cylindrical grinding wheel of radius 18 cm when rotating at 1500 rpm?
A. 14.2 kg·m²/s
B. 7.13 kg·m²/s
C. 2.81 kg·m²/s
D. 0.233 kg·m²/s
Answer















gc6 8.54
A diver can reduce her moment of inertia by a factor of about 3.5 when changing from the straight position to the tuck position. If she makes 2.0 rotations in 1.5 s when in the tuck position, what is her angular speed in the straight position?
A. 2.62 rev/s
B. 1.33 rev/s
C. 0.381 rev/s
D. 0.167 rev/s

Answer















 



B. sometimes

It depends upon the choice of the axis of rotation. If the axis of rotation is not on the line drawn through the momentum vector, as shown in the left sketch (see below), the moment arm is nonzero, and therefore L is also nonzero. If the axis of rotation is on the line of motion, as shown in the right sketch, the moment arm is zero and so is L.
























 



B. 7.13 kg·m²/s





















 



C. 0.381 rev/s