[BerntR]

Jeff,

For a starter, a real force can exist without any energy spending. For instance, when you stand on the ground, you are subject to a gravity force. It is as real as any other force, but while you'r standing, it doesn't do any work.

Regarding your curve pattern. You could put up a fence that forces the object to turn. The forces from this fence will not use any energy and they will not work. Still they will do the same "work" as the centripetal components in your examples.

In the world of golf swings & Newton, work is related to energy pretty much in the same way as acceleration is related to speed. Whenever you do work you change the mass-speed of the club or any other moving mass. (or you generate kinetic energy somewhere). When you don't do work, the energy remains constant - or is reduced due to resistance.

If you learn to see the difference between forces that work and forces that doesn't, you will get a clearer image of what swing speed is made of.