ROTATIONAL INERTIA & ANGULAR MOMENTUM

Rotational Inertia( I)  The resistance to change in rotational motion  Objects that are rotating about an axis tend to stay rotating, objects not rotating tend to remain at rest, unless an outside torque is applied (sound familiar?)  Inertia depends on mass  Torque is required to change the status of an object’s rotation. It’s the rotational equivalent to force

LINERAR vs. ROTATIOANAL  For every type of linear quantity we have a rotational quantity that does much the same thing Linear Quantities Speed Force Mass Momentum Distance Rotational Quantities Rotational (Angular) Speed Torque Rotational Inertia Angular Momentum Angle

Rotational Inertia (cont.)  Objects with mass closer to axis of rotation are easier to rotate, b/c it has less rotational inertia  If the mass is farther away from the axis, then object will have more rotational inertia, and will therefore be harder to rotate

SUMMERY  Rotational Inertia depends on mass and radius  If either one of these is large, then rotational inertia is large, and object will be harder to rotate  Different types of objects have different equations for rotational inertia  But all equations have m and r 2 in them.

Angular Momentum  Angular momentum is the “inertia of rotation”  Ang. Momentum= Rotational Inertia X Rotational Speed  Like normal momentum, but exclusively for rotation For you youngsters, an RPM is rotation per minute and we use to play records on a turn table. (stone age music)

Conservation of Angular Momentum  If no outside torque is being applied, then total angular momentum in a system must stay the same  This means, if you decrease radius, you increase rotational speed  Increase radius, then rotational speed decreases I – represents rotational inertia ω -represents angular speed

Sports Connection…  Ice skating  Skater starts out in slow spin with arms and legs out   Skater pulls arms and legs in tight to body  Skater is then spinning much fast (higher rotational speed)  Gymnastics/Diving  Pull body into tight ball to achieve fast rotation

It’s DEMO time!!!