[BerntR]

That truly is poetry in motion. I could watch that swing over and over (in fact I have watched it over and over!)

His research suggested that acceleration could be added to a swing through a motion directly opposite to the direction of the centrifugal force during the release stage of the swing. In fact, he said that this was the only way acceleration could be added at this stage. Maybe that's the rising left side we see in Hogan?

Inspired by your comment I just did a little rotation experiment with a domestic pendulum device (my daughter's passifier with a string attached). And the only way to increase the rpm is to pull it in (more or less exactly) the opposite direction.

It would be interesting to see a more accurate mechanical description of this process.

Best regards,

Bernt