Circus High Wire
How do tightrope walkers keep their balance?
Imagine yourself 20 meters (66 feet) above the ground on a platform, as thousands of faces watch and wait for you to style. Now imagine taking a step, with only a 1/2-inch metal wire between you and the ground. Welcome to the world of high wire.
High wire's roots are as old as ancient Egypt and first century China, where the art of "rope dancing" was performed over knives. In the 1850s, Jean Francois Gravelet received world acclaim for cooking and eating an omelette (complete with stove and neatly set table) on a high wire stretched over Niagara Falls.
Three different types of funambulism have evolved. Slack wire, where the rope or wire hangs a bit loose, is popular for juggling, clowning, and sword fights. Sloped wires are attached to the ground at one end and to a pole at the other, creating an angle of about 40 degrees. The most popular of all is the high-wire act, where a taut, springy wire is used to launch dizzying acrobatic tricks and phenomenal feats of balancing.
One way to view the high-wire act is to see the wire as an axis and
the center of mass of the performer as having the potential to rotate about
the axis. If the center of mass is not directly above
the wire, gravity will cause the performer to begin to rotate about the
wire. If this is not corrected, the performer will fall.
The artist often carries a balancing pole that may be as long as 12 meters (39 feet) and weighs up to 14 kilograms (31 pounds). This pole increases the rotational inertia of the artist, which allows more time to move his or her center of mass back to the desired position directly over the wire. This effect can be magnified by making the pole as long as possible and by weighting its ends.
The pole also helps balance the funambulist by lowering the center of gravity. High-wire artists use drooping, rather than rigid, balance poles. It's possible, in fact, to have such heavy weights attached to the ends of a long, drooping pole that the center of gravity of the performer/pole system is below the wire. In this case, the performer would require no more sense of balance than a person hanging from the wire.
Acrobats train for years and use mechanics to safely develop routines. Although a high-wire performance may seem like a combination of courage and magic, remember that there's a lot of work and good, old-fashioned physics thrown into the balance as well!
1. How would maintaining control over your center of balance change
as you moved from a high wire to a slack wire to an angled wire?
2. Why do squirrels have long tails?
center of mass the point at which the entire
mass of a body can be considered to be concentrated
funambulism tightrope walking-from the Latin funis (rope) and ambulare (walk)
inertia tendency of an object in motion to remain in motion and an object at rest to remain at rest
mechanics circus term for the safety wire attached to a performer executing a difficult or dangerous trick or feat
riggers circus term for the people who hang the cable and wires for performers
static not moving
to style circus term for a performer's particular way of bowing and posing to acknowledge the audience
rotational inertia the resistance of a body to a change in its rotational motion
Additional source of information
Build a tightrope setup and go for a walk!
Make your dreams of running away to join the circus come true-at least for a little while. In this activity, you'll construct a tightrope setup, learn the basics of tightrope walking, and understand a little more about the physics behind balancing! Get an adult to help you build the setup, as well as to double-check cushioning and spot you as you learn.
1. What combination of factors gave you the best balance? Why?
Here's a simple model to help you understand how center of balance and counterbalances work: Take a piece of string about 30 cm (1') in length and form it into a circle. Take a ruler and a hammer and assemble them together as shown. Balance the end of the ruler against the edge of a table with the hammer hanging below. Where is the center of balance? Why does this look like it shouldn't work?
Hold a large book in your hands. Have a friend gently try to disturb your balance. Now hold the book in different locations. Which location makes it easiest for you to keep your balance? Why?
Stand on a pillow in a safe, open, soft area. Can you balance on one foot? Now put on a blindfold. How does that affect your sense of balance?
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Educational materials developed with the National Science Teachers Association.