heedm, wow...
1) If you're going to quote me, as least do it correctly...The stiffness of the 2x4 represents the momentum of an object (the steel ball) and its tendency to want to travel in a straight line.
2) I don't know how the steel ball got attached to the 2x4, as that was never in my examples. You blended the 2 examples somehow.
3) I could have included the formula for angular momentum (L = I * w) expressed in rads and kgs/m2 (m squared)/s, included the necessary values and then performed the calculations for comparison, but that seemed like unecessary complexity for the point being made.
4) I don't see why anyone would think that a basic mechanically exerted centripetal force could cause acceleration. Any force producing acceleration must also transfer energy. In the steel ball and electric motor example, the electric motor supplies the acceleration force to get the steel ball up to speed, after that however it only supplies the force necessary to overcome the friction and drag in the system. The example could have been a frictionless system so no motor would have been needed at all after the system was spun up to speed, but since frictionless systems don't really exist...
The rope is what supplies the centripetal force, not the electic motor. What energy is the rope using to hold the ball traveling in the arc? Please understand that accleration CAN be imparted through the rope to the steel ball to speed it up, but my example is a constant speed system (after spin up). However the spin up accelerating force would be a separate force from the purely centripetal force exerted by the rope.
Really, a purely centripetal force is more like a tension (or pressure) force rather than an acceleration force. If I lean against a wall, I'm exerting pressure (or tension) on the wall, but I'm not transferring any energy to it (unless the wall moves). Similarly, the "tension" in the centripetal/centrifugal system is the tendency of a body in motion to travel in a straight line.
Pulling a moving object into an arc is similar to pulling a rubber band, and to stretch the rubber band further, requires that more tension force be applied. In the same way, pulling a moving object into a tighter arc also requires more centripetal force (assuming momentum stays the same). If you let go of the rubber band it will return to its normal length. Let go of a moving object traveling in an arc, and it will return to traveling in a straight line without any change in its momentum.
This is why I believe that the centrifugal force is as real as the centripetal force. They are both "tension" forces, and neither is an acceleration force. The purpose of the 2x4 in the previous post was to illustrate the "tension" in the centripetal/centrifugal system.
(edited for additional clarity)
[ 24 December 2001: Message edited by: Flight Safety ]</p>