On 26.06.19 08:14, Gregg Eshelman via Emc-users wrote: > I've read that centripetal force is "pushing inward" which sounds like > utter baloney to me. When anything is spinning, nothing is pushing > inward.
It's easiest to analyse with a simple example, e.g. a nut tied on the end of a string, which you're whirling about your head. The mass only describes a circle because the string exerts inward (centripetal) force to change the velocity from the straight line it would otherwise follow. Let go the string, and the nut whizzes off at a tangent to its last point in orbit, reverting to the straight path. While it's orbiting, it is the pull on the string which creates the "opposite and equal" centrifugal force. It does so because it is accelerating the mass, and f = ma. When you let go, you've set the centripetal force to zero. The tension in the string falls to zero, i.e. no centrifugal force either. What flings the nut, then? It's just momentum - nothing more. It departs at a tangent, in a straight line. Try it with a sling, as used in the bronze age. > It's going around in a circle with every atom attempting to > fly outward. Well, that's contrary to observable physics. A body at rest just sits there, and a moving body will continue in a straight line until acted on by a force. It is the continuous acceleration (velocity vector angular change) caused by the centripetal force exerted by the string which is creating circular motion. > If the spinning thing is hollow and there are loose > objects inside it, such as people, those objects are being forced > outward by the centrifugal force while the material composing the > outer parts and the inner surface resists that outward force - as long > as structural integrity doesn't fail. The loose objects, if suddenly released, would travel in a straight line. It is the containing wall which accelerates then onto the circular path, just as a rope to the centre would. Circular motion is a result, not a cause. > If a spinning object's integrity fails, the broken bits fly off at > tangent vectors which can be calculated based on rotational speed, > angular velocity, and mass of the fragments. Yup - just momentum. And the "tangent vectors" are straight lines. > Force requires motion, or the energy expended *attempting* to produce > motion. s/motion/acceleration E.g. the acceleration of bending a straight line path into a circle. That only happens with centripetal (centre seeking) force. Focus on this part, and the penny drops. It should be clear by now, I figure. (Apologies to Andy - I figure he'd explain it more clearly.) Erik _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
