Wednesday, May 28, 2008

Falling at Supersonic Speeds: Weightless or Not?

There are many stereotypes of the French, but a relentless ambition to fall towards earth at dangerously high altitudes isn't one of them. Michel Fourier, a retired French army officer intended to do just that, by sky-diving from a small compartment suspended beneath a helium-filled hot air balloon.

Aside from breaking numerous records, he would have been the first human to break the sound barrier by falling at supersonic speed. Unfortunately, his balloon detached itself while being inflated and cancelled his mission.

There is an interesting error found in the print version of the New York Times articles on Michel Fourier, that was removed in the online version:

"An article on Saturday about Michel Fournier, the retired French army officer with plans to sky dive from a balloon gondola 25 miles above the earth's surface, misstated the point during his journey at which he expects to experience weightlessness, and misstated the altitude at which his parachute was designed to open. He would experience weightlessness during descent, not while in the balloon's gondola. And his parachute is designed to open around 5,000 feet, not 20,000 feet."

The original statement about "experiencing weightlessness while in the balloon's gondola" is the interesting part here, even if it was retracted. It's a good example of the vague confusion surrounding the concept of weightlessness. There is a notion that simply being high enough above the planet leads to weightlessness. But weightlessness is not caused by the distance from earth! The International Space Station is a mere 250 miles above the earth, where gravitational attraction is only 10% less than on the earth's surface.

Astronauts at the International Space Station experience weightlessness because they are orbiting the planet, not because they are above it. It is being in orbit that causes you to feel weightless, or gives the impression of floating, when in fact you are constantly falling around the earth.

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