Sunday, September 20, 2009

The Force is Strong With This One

We say that astronauts in space are experiencing “zero-gravity,” but there is really no such thing, not in our universe anyway. The weightlessness that astronauts experience is actually a state of constant free fall, which is caused by the presence of gravity, not the lack of it.

Astronauts at the space station float around freely, seemingly unaffected by any sort of gravity, but it's an illuuuusion...

Yet we have images and videos of astronauts floating about in and around space stations; they aren’t being pulled toward the Earth and neither is the space station. One might be compelled to say, "How can anyone claim there is no such thing as zero-gravity when NASA has 'zero-gravity' simulations and testing for astronauts?" Many scientists regret the use of the term 'zero-gravity' for this very reason; it's misleading.

The astronauts and the space station are actually falling together, always at the same rate (equally accelerated by gravity), so they only appear weightless. It’s the same with satellites and celestial bodies; they are always influenced by gravity. In fact, there is no place in our universe where gravity does not exist, because gravity is a property of mass, not some disembodied force. Everything that has mass also has gravity, including you.

The space station is traveling horizontally, while also being pulled toward the center of the earth by the force of gravity. The result is the curved trajectory that we call "orbit." Objects are not drawn to scale. For a scale, see the next illustration.

Constant free fall works because objects in orbit (like the moon, the space station, and satellites) are traveling horizontally as well as vertically (relative to the surface of the earth). Imagine that you are up incredibly high (more than 200 miles up, so you don’t have to worry much about air resistance) and are moving forward with incredible speed (more than 17,000 miles per hour).

The force of gravity is constantly pulling down on you, but the earth is not flat, it curves away from you. As you’re falling, the Earth is literally retreating beneath your feet, so you never hit land. You're falling at an angle that matches the curve of the earth. This is constant free fall.

Imagine this (only imagine, do not attempt): You are going to jump off the edge of a cliff, riding on a bathroom scale (repeat – only imagine). You leap off the ground with the scale at your feet, and you try to read the little dial telling you your weight. Since you and the scale are both falling at the same rate (remember Galileo dropping things off of the leaning tower of Pisa to show that size makes no difference to how fast you fall?), the scale would register a whopping nothing! You have achieved the appearance of weightlessness.

A thought experiment where a person on a scale (there it is) falls off the edge of a cliff, demonstrating how the appearance of weightlessness is created while gravity is still acting on the body. This is not to be attempted outside of your imagination.

Although the term “zero-gravity” is thrown around with abandon, it is a really the opposite of what is happening to the space station and the astronauts inside. Without the force of gravity pulling objects toward one another, the space station, satellites, and even the moon would just fly off into space, never to be seen again.

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1 comment:

  1. i heard neil tyson degrasse say "zero gravity" on his "star talk" podcast recently. i think i died a little inside.