On Friday 20 July 2007 00:03, Bill Hooper wrote: > * The equation uses, for the effective length of a pendulum, the > length from the support to the center of the spherical weight and > Wilkins gives it as: > length = d + 0.4r > where d is distance from support to center of the spherical bob and r > is the radius of the (spherical) bob. (and the factor of 0.4 is just > 2/5.) Actually, Wilkins uses x in place of r in the above. I think > this is an error, possibly just typographical. I think x is supposed > to be the extra length that needs to be added to the length of the > pendulum (measured to the center of the bob) to obtain the effective > length of the entire pendulum. If I am correct then his d+0.4x should > be d+0.4r instead.
d+0.4r is not right. Moment of inertia is kg*m^2. The moment of inertia of the pendulum has two components: the mass of the bob times the square of the length, and the m.i. of the bob. To add the m.i.s, you don't add the lengths; you take the Pythagorean sum of the lengths. Pierre
