Why are Astronauts Weightless in Space?

If you watch a video of astronauts inside the International Space Station or similar ones, you’ll notice that they float in space like there were no gravity. They are living in a so-called “zero gravity” environment.

But is it true that there’s no gravity up there?

Although some sources might suggest that there are no gravitational forces whatsoever at work in space, the true answer is: Gravity is everywhere – especially in orbits around massive bodies like the Earth (or the sun, or a star in general, or the center of galaxies, and so on… you get the idea)! The term “zero gravity” associated with the interior of a spacecraft or an experiment inside the ISS is very misleading, I think. As a matter of fact, the astronauts would feel and float in the same way, if they weren’t on a track around the Earth, but instead freely floating through outer space. “Orbiting the Earth” and “zero gravity” are kind of the same thing for astronauts inside the spacecraft. If there were no windows, the passengers would likely be unable to say whether they are circling around a celestial body or fly though empty space. But if we talk about “zero gravity” on the International Space Station, we might risk to confuse ourselves, because there definitely is gravity at places like the space station’s orbit!

Chris Cassidy and Karen Nyberg in the Cupola of the International Space Station, 7 Aug. 2013. (Credit: NASA)

But why, however, do astronauts float like there were no attracting forces inside the spacecraft?

The answer is that they and their spaceship are freely falling around the Earth. And as it is, you are weightless in free fall.
To understand how that’s possible, consider a javelin thrower: He pitches the spear as far as possible. If he is one of the best of his kind, it will land some 100 meters (about 330 feet) away. If the thrower is much better (like Kermes, the Persian athlete in “The Twelve Tasks of Asterix“), he might be able to pitch his spear across the ocean. Then, it will already “feel” the curvature of Earth: It will take a little bit longer for the spear to hit solid ground again, because the Earth’s surface “bends away” from the spear. The further the javelin flies the longer it is “up in the air” – just because of the curvature of our planet.
But now consider Obelix, the superhumanly strong Gaul, who can pitch a spear much further than anyone else. A spear thrown by him will never see solid ground again – it will circle around the Earth.

You don’t believe me? – Here’s my video proof (it happens shortly after 16:50 mins!):

Now you know how the Internation Space Station is put into orbit – the only thing you have to do is to substitute Obelix by a powerful rocket and the spear by the spacecraft. 😉

Here’s is another video which gives much better answers to the question “Is there gravity up there?” than I did.  (I stumbled upon it in the great German blog “Astrodicticum Simplex” by Florian Freistetter.)

Have fun with this scientific parasite inside Wil Wheaton’s brain! 😉


About tempse

I think about physics, other stuff, and physics. Besides, I share some thoughts on the internet.

Posted on August 14, 2013, in Earth, physics, universe, video and tagged , , , , , , , , . Bookmark the permalink. 2 Comments.

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