MOVING EXPERIENCES: BIKES, GYMNASTICS, ROCKETS
Question. Most things in life are easier said than done. But some are the other way around—easier done than said. Rocking on swings is an example. Exactly how does a child pass the energy of his muscles to swinging? The answer is not that obvious.1
Answer (the anatomy of a resonance). Imagine yourself rocking back and forth on swings. You feel the greatest g force when zooming past the bottom of your path. By the same token, the least g-force is near the highest points of your trajectory2 Imagine now holding a weight in your hand, resting it your lap, Figure 6.1. When you are passing the bottom of your trajectory, raise the weight to your shoulder; keep it there until you are near the top of the trajectory and once there quickly lower it back. Repeat: lift when passing
1 A little boy asked: [Grandpa, do you sleep with your beard over or under the blanket?] That night, the sleepless grandpa was lying on his back, trying his beard this way or that and cursing. Neither way felt right any more.
2 There is a [double whammy] responsible for the lesser g-force at the top of the trajectory: (1) the centrifugal force is smaller, and (2) gravitational force's component is smaller.