Section 2 review
Rotational inertia is at the heart of the rotation of rigid bodies. The moment of inertia of an object represents its rotational inertia about a particular axis. Moment of inertia depends not just on mass but also on the distribution of that mass. Even if a solid sphere and a hollow sphere have the same mass, they have different moments of inertia because their mass is distributed differently. Rolling objects possess not just kinetic energy but also rotational energy (sometimes called the kinetic energy of rotation). When rolling downhill, objects will be accelerated differently, depending on their moment of inertia. Read the text aloud
rotational energy, precession

E r = 1 2 I ω 2

Review problems and questions

  1. In bowling, usually the bowling ball will initially slide down the lane without spinning. Partway down the lane, however, the ball begins to roll. What happens to the velocity of the ball when it begins to roll? Read the text aloud Show
  1. What is the moment of inertia for each of the following? (Mass of the Earth: 6.0×1024 kg. Mass of the Moon: 7.3×1022 kg. Radius of the Earth: 6.4×106 m. Radius of the Moon: 1.7×106 m. Radius of the Earth’s orbit around the Sun: 1.5×1024 m. Radius of the Moon’s orbit around the Earth: 3.9×108 m.)
    1. Moon’s orbit around the Earth
    2. Earth’s orbit around the Sun
    3. rotation of the Moon about its axis
    4. rotation of the Earth about its axis Read the text aloud Show
  1. A beginning bowler pushed a 6 kg bowling ball so that it rolled down the lane without slipping at 2 m/s. How much work did the bowler do on the ball to start it rolling? Read the text aloud Show
  1. Will a hoop or a solid disk be accelerated more when rolling down the same inclined plane? (Assume that the two objects have the same radius.) Read the text aloud Show
Two designs for a wheel and axle system
  1. You are considering two different designs for the wheel that forms part of a wheel-and-axle simple machine. Although both designs have the same mass, one puts most of the mass near the rim while the other distributes the mass evenly throughout the wheel. What are the advantages or disadvantages of each design if the input force will be applied to the axle? Read the text aloud Show

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