These last three experiments will focus n how energy is stored in the rotation of an object. You know that if you do work W = F*D on a ball (for instance), starting from rest it will move in the direction of your force. And, if it is a point object, then the object will have an energy K = 1/2 m v*v which is equal to the work you have done.
Several of you found in the last experiment (and review) that the energy was consistently a little *less* than you would expect from the EP. For any object rolling without slipping, the rotational velocity, omega, and its linear speed v are related by v = omega * r, where r is the radius of the object.
The object as it rotates has an energy (because each of its atoms if moving in a circle, each of the atoms has mass, so you can add up the kinetic energies of each bit of mass), and that energy (Chapter 9) is K = 1/2 I * omega * omega, where “I” is the moment of inertia of the object. It acts like the “mass” for rotations.
The total energy of the object is then: E = 1/2 m * v^2 + 1/2 I * omega^2, with omega = v/r.
I want you to do an experiment in which you can measure from tracker what is the total work done to an object, and by assuming the above to measure the moment of inertia of the object. The book has various estimates for I for some objects of mass M and radius r (hoop= M r^2, solid disc = 1/2 M r^2, hollow ball 2/3 M r^2, filled ball, 3/5 M r^2) but your object is only approximately one of those objects.
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