Section 1 review
Motion can be translational, rotational, or both. Rotating objects move about an axis of rotation that can be located either inside or outside their body. Just as a mass has inertia that resists changes in its linear motion, the same mass has rotational inertia that resists changes in its rotational motion. Angular momentum is the rotational analog of linear momentum, is expressed by the letter L, and is conserved in the absence of any net external torque. Every object has a center of mass, which can be located either inside or outside its body. Many athletes take advantage of rotation about their center of mass, and conservation of angular momentum, in performing impressive feats. Read the text aloud
axis, rotation, revolution, translation, rotational inertia, moment of inertia, angular momentum, linear momentum, conservation of angular momentum, center of mass

I=m r 2
L=r×mv
L=Iω

Review problems and questions

  1. When you throw a spinning plastic disk, such as a Frisbee®, why can it fly so far without tipping over sideways? Read the text aloud Show
  1. The geographic center of the contiguous 48 states in the USA is the two-dimensional mean (or average) location of the land mass. How could you use a piece of poster board to locate the geographic center of the USA? Read the text aloud Show
  1. A tall office worker doesn’t like to lean over to reach things, so he decided to load all his files into the top drawer of his filing cabinet, leaving the other drawers empty. Is this a good or bad idea? Why? Read the text aloud Show
  1. Where is the center of mass of the letter “L” located? Read the text aloud Show
  1. Why does a tightrope walker’s horizontal pole usually droop at the ends? Read the text aloud Show
  1. Judy is conducting an investigation by spinning washers (with a total mass of 100 g) attached to a string over her head. When the washers follow a path of 30 cm in radius, she spins them at one revolution per second.
    1. What is the angular velocity of the washers in radians per second?
    2. What is the linear velocity of the washers?
    3. What is the angular momentum of the washers?
    4. She then pulls on the string and shortens the radius at which the washers are rotating to 10 cm. What is the new angular momentum of the washers?
    5. What is the new angular velocity of the washers? Read the text aloud Show

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