June 15, 2012 -- intro: Nik Wallenda trained long and hard to prepare to walk a thin wire across Niagara Falls, practicing against the spray of a fire hose and gusts from a wind machine to recreate some of the conditions found above the cascades.
Click through to watch simulations of what Wallenda will confront and the measures taken to stabilize the wire against the forces of nature.
quicklist: title: Different Microclimatestext: Wallenda will encounter different microclimates as he traverses Niagara Falls. Once he crosses the brink -- the edge of the falls -- the microclimate there begins to create downdrafts.
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quicklist:title: Drafty Conditionstext: As Wallenda crosses the gorge, there will be additional downdrafts created by the force of the waterfalls crashing down on the Niagara River and kicking winds back up again. He will also face mist caused by the vaporization of the water from the force of the falls.
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quicklist:title: Bundled for Strengthtext: The cable Wallenda will walk is two inches in diameter -- about the width of three pennies -- and made up of 343 high-strength steel wires. At the center is the king wire: It's a tiny but mighty wire just one-75 thousandths of an inch in diameter.
Six identical wires fit perfectly around the king wire to form a bundle. That bundle is surrounded by six other bundles and then that core is surrounded by six more bundles with wires of varying sizes.
Why hundreds of tiny strands instead of larger ones? Because if one wire fails, its crack won't spread to its 342 neighbors.
quicklist:title: Pendulum Powertext: The wire rotates easily so Wallenda's team installed 50-pound pendulums at 150-foot intervals. The downward weight prevents the wire from rolling.
quicklist:title: Waves and Bouncestext: The wire will bounce about an inch up and down from the impact of Wallenda's footfalls, creating waves that will move back and forth on the wire, sometime colliding and creating a surprise bump.
To minimize that effect, engineers mounted shock absorbers on either end of the wire.
quicklist:title: Bad Vibrationstext: The wire is vulnerable to what's called an Aeolian vibration, a flutter from the wind, similar to the movement of police tape on a windy day. Engineers have hung 20-pound dampers that bounce on the wire to counteract and dull that vibration.