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Phy 1405
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Key Concepts:
1.
Rotational Inertia
2. Angular Velocity
3. Torque
4. Center of Mass
5. Moment of Inertia
(rotational mass)
Phy 1405
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Observations About Seesaws
•
A balanced seesaw can remain horizontal
•
A balanced seesaw rocks back and forth easily
•
Two equal-weight children balance a seesaw
•
Two unequal-weight children don’t balance
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But moving the heavy child inward helps
Phy 1405
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Question 1
How exactly does a balanced seesaw
behave?
– Is a horizontal seesaw balanced?
– Is a balanced seesaw horizontal?
Phy 1405
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Physics Concept
•
Rotational Inertia
– A body at rest tends to remain at rest
– A body that’s rotating tends to keep
rotating
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Physical Quantities
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Angular Position – an object’s orientation
•
Angular Velocity – its change in angular position with
time
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Torque – a twist or spin
Angular Position
2
π
radians in a full circle
Axis of Rotation
Angle of
Rotation
Phy 1405
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Newton’s First Law
of Rotational Motion
A rigid object that’s not wobbling and that is
free of outside influences rotates at a
constant angular velocity.
A rigid object that’s not wobbling and that is
free of outside torques rotates at a constant
angular velocity.

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