It helps to have some intuitive understanding of balance when adjusting the acrobat cyclists. There are three steps to the adjustments: getting the acrobats to stay upright, keep them from tilting and (if you want to) have them ride on one wheel (a wheelie).

It's possible to balance a stick by finding the point where half the weight is on one side and half on the other side. If you move the pivot point either way, the heavier side dips down.

The acrobats work the same way. The critical pivot point is at the bottom of the wheels where they meet the string. If more than half the weight of the whole unit is below the string, then the acrobats will stay upright. So getting the acrobats to stay up means bending the bar down on both sides until the "center of gravity" is below the bottom of the wheels. Notice that the acrobats take up a lot of space to give the illusion of being top heavy, but they don't weigh much. The weight is densely packed at the ends of the bar.

The next question is how to adjust the weight if the acrobats lean to one side. The further out horizontally a weight is, the more leverage it exerts to tip the acrobats that way. The illustration is quite exaggerated, but it shows how you can balance the acrobats any way you want, even if the weights aren't equal.

To make them ride on one wheel, bend the bar so that both weights are toward and then past one of the wheels until they tip. The problem with riding on one wheel is that unless you move gently it will fall off the string. There is a classic tin toy like the acrobats except that it is a unicycle. The legs of the clown are attached to the pedals of the unicycle. I speculate that this is to slow it down a bit so it doesn't jump the string.

Here's a great link of a video at a science museum with a unicycle that ordinary people actually strap into and pedal on a wire, high above the floor. It doesn't require skill because it has a weight/balance arrangement similar to the acrobat toy. Thanks Yellow Springs School. Click here.

The concept of keeping your center of gravity low extends well beyond acrobatics. It's important in sports like wrestling and (American) football so the players don't get knocked over. Some sports utility vehicles (SUVs) have been criticized as having a center of gravity that's too high, causing them to roll over more easily.

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