13.1 - Rotation and angular momentum

Objects with angular momentumSpinning objects tend to keep spinning for the same reason moving objects tend to keep moving with the same speed and direction. A spinning bicycle wheel has angular momentum as a result of its rotational motion. Angular momentum resists changes in rotational speed or orientation, similar to the way linear momentum resists changes in linear speed or direction. If you spin a heavier wheel at the same speed, or spin the same wheel faster, it will have more angular momentum and be more difficult to stop or turn. Angular momentum plays a key role in the behavior of objects from the smallest microscopic scale inside the atom to the largest macroscopic scales in the dynamics of the Solar System and the Milky Way Galaxy. Read the text aloud
Describing rotational motion
Translational and rotational motion of a rolling ballObjects may move from one place to another while they are simultaneously rotating. A good example is a rolling ball. The ball has translational motion that takes it across the floor. Translation is a type of motion that causes a change in position. While the ball is translating it is also rotating. When we analyze complex motion we may treat translational and rotational motions independently and associate momentum and energy with each. Read the text aloud Show Oscillatory motion
The axis of rotation is an imaginary line around which rotation occurs. A spinning top rotates about a vertical axis—a straight line—passing through the center of the top. The axis of rotation for a bicycle wheel is the axle of the wheel, which is horizontal when the bicycle is being ridden. Read the text aloud Rotational top for a spinning top
Many properties of rotational motion, such as angular momentum, depend on the location and orientation of the axis of rotation. The same object rotated around a different axis will have different rotational kinetic energy and angular momentum, even if the mass and rotational speed stay the same! Read the text aloud
The Earth <i>rotates</i> about its axis and <i>revolves</i> around the SunA rotation describes a motion in which the axis lies within the object, such as the motion of the spinning top or bicycle wheel. A revolution refers to a rotational motion about an axis that is outside the object. As an example, Earth undergoes both rotation and revolution. Earth makes a full rotation about its north–south axis every 24 hours, creating day and night. Earth makes a full revolution (orbit) around the Sun once per year. The axis of Earth’s orbital motion passes through the Sun and is perpendicular to the plane of the Solar System. Read the text aloud
Does the Moon rotate or revolve every lunar month? Show
What kind of motion occurs when
  1. you ride a bicycle down the street?
  2. you mount the bicycle on a repair stand and spin the rear wheel?
  3. a ball skids across the floor?
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