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## Rotational Motion of an Object

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**Rotational Motion of an Object**Physics Matters: Chapter 7**Rotational Motion**• All Spinning Objects • Axis of Rotation • The line about which everything rotates. • Speed of Rotation • Period of rotation • The time of a single complete rotation (T) • Frequency of rotation • The number of cycles completed in a given time (f = hertz) • Period = 1/Frequency or Frequency = 1/Period • T= 1/f f=1/T**Spinning**• Angular speed • = s/r ( is measured in radians) • For 360 degreed, s = 2r • 3600 = 2 radians • Angular speed = 2f**Torque**• Tangential force being applied times the perpendicular distance from the axis of rotation • = Ftr**Angular Momentum**• Moment of inertia • In general, the farther away a mass is from the axis the greater its moment of inertia is. • I = kmr2**Angular Momentum (Cont.)**• Momentum of inertia times angular speed • L = I • Conservation of Angular momentum • Direction of Rotation • The right hand rule**Center of GravityCenter of Mass**"All of science is nothing more than the refinement of everyday thinking."-- Albert Einstein**Center of Gravity**• Point of an object located at the average position of weight.**Center of Mass**• The Average position of matter**Toppling**• Toppling occurs when the center of gravity extends beyond the support base.**Stability**• Unstable – CG is lowered with displacement • Stable – work must be done to raise the CG • Neutral – displacement neither raises or lowers the CG**Objects rotate around their center of gravity.**Let’s try some activities!!