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!
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. Materials
- one 8'-long two-by-four board
- two 4'-long two-by-four boards
- two smooth poles, one about 3' long, the other about 6' (The length doesn't have to be exact, so long as the two sticks have about 3' difference between them.)
- 3" nails
- soft, grassy area or cushioned mats
- 2 half-gallon plastic jugs filled with water
- 50 cm (20") of string or cord cut into two equal lengths
- Place the two-by-fours on their thinner edges, forming an H (see illustration). Center and nail the shorter boards onto the ends of the longest two-by-four. Sand down the entire surface, making sure there are no rough edges or slivers.
- Place your "tightrope" on the soft, grassy area. If you put it on cushioned mats, make sure there is enough padded area to protect your entire body if you fall.
- First, try walking from end to end very slowly. Where do you find yourself holding your hands and arms? Try holding them still-first straight out from your body, then overhead, then stiff by your sides. How do these different positions affect your balance? Why? Try these same positions holding a filled plastic milk jug in each hand. Does the added weight make balancing easier or harder? Why?
- Try walking your tightrope with your longer pole. Move your hands together until they touch in the middle of the pole and walk the tightrope holding the pole horizontally. Now spread your hands as far apart as possible on the pole and walk the tightrope again. Does your hand position affect your ability to balance? How? Why? Try the two hand positions again with a broom. Is there any difference? Why?
- Using the hand position you found to be the best for balancing, try walking your tightrope first with your short pole, then with your long pole. Which length helps you balance better? Why?
- Tie the filled plastic milk jugs to the ends of your long pole and walk the tightrope again. Do the weights affect your balancing ability? How? Why?
- Using the short pole, walk across your tightrope. What happens to the pole when you start to lose your balance? What happens to your body? Can you use the pole to deliberately make yourself lose your balance?
- Add some tricks to your repertoire. Try walking backwards from end to end, balancing on one foot, or turning around on one foot. Can you think of other tricks you can add with practice? (Here are a couple ideas-try stepping over your balancing pole, or playing with a hula hoop.) Question 1. What combination of factors gave you the best balance? Why?