Lazy flies

Article in today’s Sunday Times. Not of much interest to anyone except those who might have an opinion on the use of the word ‘inertia’.

And while we’re on the subject, here’s a diagram illustrating different ‘moments of inertia’ for a solid disk versus a thin pipe. Two wheels of the same mass and radius roll down incline. Different speeds are recorded. Different moments of inertia are calculated.

Total Energy = Potential Energy at the top of the board = Translational Energy (m*v*v/2) + Rotational Energy (I*w*w/2). Since the hoop has an I value of M*R*R and the wooden disk is half that, the hoop will only have 3/4 of the velocity of the disk at a particular height. By the equation V2=V2o+2a(x-xo), the distance the hoop travels by a particular time will be the square root of 3/4 times the distance travelled by the disk.

Hope you’ve got that.

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