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/ff=1/T

Spinning Angular speed  = s/r (  is measured in radians) For 360 degreed, s = 2  r = 2  radians Angular speed = 2  f

Torque Tangential force being applied times the perpendicular distance from the axis of rotation  = F t r

Angular Momentum Moment of inertia In general, the farther away a mass is from the axis the greater its moment of inertia is. I = kmr 2

Angular Momentum (Cont.) Momentum of inertia times angular speed L = I  Conservation of Angular momentum Direction of Rotation The right hand rule

Center of Gravity Center 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!!