Rotational Dynamics (moment of inertia and the action of torques)

Parallel-Axis Theorem

[M | t+ | — ]
The period of oscillation of an object doesn't change for different suspension points, as long as they're the same distance from the COM.

[In-Depth Description]

Hula Hoop Rotational Inertia

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A suspended hula hoop has the same period of oscillation as a pendulum whose length is equal to the diameter of the hoop.

[In-Depth Description]

Tennis Racquet Flip

[M | t | ★★★]
Demonstration of stable and unstable axes of rotation.

[In-Depth Description]

Spinning Football/Coconut

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Preferred axis of rotation for stability.

Rotational Stability

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A chain or rope (lariat), when rotated fast enough, assumes an axis about which its moment of inertia is maximum.

Angular Impulse

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Wheel is made to rotate by falling weight attached by string.


[S/M | t | —]
A top that flips upside down raising its center of gravity and reverses spin.


[S | t+ | —]
This object, when given a spin, seems to defy the laws of angular momentum as it stops spinning, rocks in place, and proceeds to spin in the opposite direction.

Torsion Pendulum

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Determination of the moment of inertia by period measurements.

[In-Depth Description]


[L | t | ★★]
A very large cable spool (or smaller version) is made to roll in either direction or slide, depending on the angle of pull; action of a torque.

[In-Depth Description]

Which Way Will the Bike Move?

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A puzzler concerning torques - pull on a rope attached to the pedal and figure out the consequences.

Rolling Down an Incline

[L | t+ | ★★★★]
Various objects are raced down an inclined plane to verify the effect of their moments of inertia.

[In-Depth Description]

Torque Stick

[M | t | ★★]
Have students literally feel the increase in torque as the lever arm is increased.

Rotating Rod

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A rod with adjustable weights (moment of inertia) is made to rotate by a falling weight attached to the axle via string.

[In-Depth Description]

Center of Percussion

[M | t+ | ★★]
The motion (or lack of motion) of the suspension point of an object is observed when the object is struck a blow.

[In-Depth Description]

Breaking Broomstick on Wineglasses

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Two wineglasses support a broomstick which is given a swift blow with a pipe. The broomstick, but not the glasses, breaks.

Falling Faster than 'g'

[M | t | ★★]
Allow a stick to rotate under the force of gravity and the free end will accelerate at a rate greater than g. Relation between angular acceleration and linear acceleration seems to give free-fall paradox.

[In-Depth Description]

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