ROTATIONAL INERTIA & ANGULAR MOMENTUM. Rotational Inertia( I) The resistance to change in...
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Transcript of ROTATIONAL INERTIA & ANGULAR MOMENTUM. Rotational Inertia( I) The resistance to change in...
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 SpeedForceMassMomentumDistance
Rotational QuantitiesRotational (Angular) SpeedTorqueRotational InertiaAngular MomentumAngle
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 r2 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 http://www.youtube.com/watch?v=AQLtcEAG9v0
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!!!