For best results use a 200g or 500g weight.

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Determination of the moment of inertia by period measurements.

What it shows:

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

How it works:

The parallel-axis theorem allows us to readily deduce the rotational inertia of a hoop about an axis that passes through its circumference and is given by

I = I_cm+MR² = 2MR²

where M is the mass of the hoop and R is its radius. The period of oscillation thus becomes T = 2∏√(I/mgd) = 2∏√(2R/g), which is equal to that of a pendulum whose length...

What it shows:

One can show that 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. This is consistent with what the parallel-axis theorem tells us about the moment of inertia of the object.

How it works:

The parallel-axis theorm states that if I_cm is the moment-of-inertia of an object about an axis through its center-of-mass, then I, the moment of inertia about any axis parallel to that first one is given by I = I_cm +...

A motor driven gyro hidden in a suitcase gives surprising results when the suitcase is moved.

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Small gyroscope used primarily as a stage prop in discussion.

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Lecturer tries to swing baseball bat while standing on turntable.

Rotating balls change speed as radius of rotation is changed.

A pendulum is allowed to "crash" into a bar, dramatically altering its motion, but energy is conserved as is evidenced by the return swing.

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Same as previous except that mass ratio of balls is 1:3 (softball:basketball) leaving basketball dead and softball four times the height.

A tennis ball/basketball combination is dropped to the floor ... the tennis ball theoretically bounces to nine times the original drop height.

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A wound-up spring propels a toy truck.

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Single seat CO₂ powered rocket cars.

Photo by Rose Lincoln

The choice of propellant for this toy rocket makes a huge difference in thrust.

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A motorized fan mounted on a reaction cart blows air into a "sail" which is also mounted on the cart. Which way will the cart move?

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