[no_mind_golfer]

nmgolfer

What do you think of his centripetal arrow pointing towards the swing center in his diagram?



The presumption is that the swing center is the center of the clubhead's arc of travel. However, it is nowhere near the center of a circle transcribed by the clubhead arc.

Here is Tiger Woods clubhead arc - only roughly outlined in red. Blue is the swing center. Yellow is the radial distance to different points on the clubhead arc.



What do you think of Bernt's statement "that centripetal force conserves speed and stores energy"?

Surely centripetal force is only relevant to the clubhead's circular motion at each instantaneous moment in time - as it constantly changes direction in a circular manner, and moves from one point on the clubhead arc (point X) to another point (point Y), and the centripetal force is the force needed to centripetally accelerate the clubhead from point X to point Y. The direction of the centripetal force is surely drawn towards the center of the instantaneous circle of rotation, which changes from moment-to-moment because the clubhead arc is not perfectly circular.

Jeff.

Jeff...

I do not understand those yellow lines. The center of curvature depend on the path (kinematics) not the golfers body or somebody's perceived swing center.

Consider for instance the simple circle, which is just a special case of an ellipse. For a circle the instantaneous center of curvature is always the center of the circle and it doesn't ever deviate from that position. The radius of curvature is just the radius of the circle and it never deviates. Now consider an ordinary ellipse where that has different major and minor axis. (see image)




I the case of the ellipse the radius of curvature rarely points to the center of the ellipse and both the location of the center of curvature and the magnitude of the radius of curvature are constantly changing. This constant change scenario is the case for the vast majority of curves be they hyperbola, parabollas ellipses, spirals or general 3d space curves (which is what the golfer's hand path and club head path are)

I think this from the centripetal force wiki is good stuff

Centripetal force should not be confused with centrifugal force. Centripetal force is a kinematic force requirement deduced from an observed trajectory, not a kinetic force like gravity or electrical forces. Centripetal force requirements may be deduced from a trajectory in any frame of reference (although the trajectory of an object and the deduced centripetal force will vary from one frame to another). Because centripetal force is a kinematic force requirement inferred from an established trajectory, it is not used to deduce a trajectory from a physical situation, and centripetal force is not included in the inventory of forces that are used in applying Newton's laws F != m a to calculate a trajectory.

The centripetal force always points in the direction normal (perpendicular) to the path at any instant towards the instantaneous center of curvature. That location would rarely if ever be a golfer's body part (left shoulder... spine etc....) Its a location in space determined solely by the path of the object.

Also... as the words "centripetal force requirement" imply, its something that is required to keep an object rotating but not something that does work (force through distance = work) or stores energy.

Energy comes in the forms of Kinetic or Potential... Its not "stored per se" in the golf swing anywhere in my mind.

PS .... This is really good stuff from that same wiki... we don't use rotating reference frames in golf... therefore CF should be purged from the lexicon.

Centrifugal force, on the other hand, is treated in a rotating frame as a kinetic force, that is, as part of the inventory of forces used in Newton's laws to predict motion. Centrifugal force is a fictitious force, however, that arises only when motion is described or experienced in a rotating reference frame, and it does not exist in an inertial frame of reference.[4]