2.1 Seesaws

2.1 Seesaws - Observations About Seesaws • • • •...

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1 Phy 1405 1 Key Concepts: 1. Rotational Inertia 2. Angular Velocity 3. Torque 4. Center of Mass 5. Moment of Inertia (rotational mass) Phy 1405 2 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 • But moving the heavy child inward helps Phy 1405 3 Question 1 How exactly does a balanced seesaw behave? – Is a horizontal seesaw balanced? – Is a balanced seesaw horizontal? Phy 1405 4 Physics Concept • Rotational Inertia – A body at rest tends to remain at rest – A body that’s rotating tends to keep rotating Phy 1405 5 Physical Quantities • Angular Position – an object’s orientation • Angular Velocity – its change in angular position with time • Torque – a twist or spin Angular Position 2 π radians in a full circle Axis of Rotation Angle of Rotation Phy 1405 6 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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2 Phy 1405 7 Angular speed = change in angle/ time An object turning at 1 radian-per- second completes a full circle in just less than 6.3 seconds Right Hand Rule Angular Acceleration the change in angular velocity with time Phy 1405 8 Balanced Seesaw • A balanced seesaw – has constant angular velocity • It’s angular velocity is constant when it is – motionless and horizontal – motionless and tilted – turning steadily in any direction Phy 1405 9 Question 2 Why does the seesaw need a pivot?
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2.1 Seesaws - Observations About Seesaws • • • •...

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