If you're having trouble keeping the sled floating next to you, perhaps it will help to understand why leaning in one direction causes the sled to move in that direction. (Note the series of photos opposite.)
It's easier to conceptualize what is happening if the arm links can't boom up or down. Imagine a series of fixed horizontal links connected by vertical pins and bearings and free to rotate. One end is fixed (to your body), and on the other end is a weight. It's analogous to those wooden, segmented snake toys.
If the pins are all vertical, the weight will be content to remain wherever it is placed within its range of motion. But if the pins are not vertical, the weight will instantly try to straighten ...
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