Deakin Communicating Science 2016

EES 200/101

Misconceptions of Great Gravity: The Bottomless Pit

How do astronauts float? Weightlessness and zero gravity?

Let me entertain an idea here.

We’ve all heard of the concept of a bottomless pit! Maybe you’ve seen one in a cartoon where the characters just fall endlessly, or perhaps you’ve imagined yourself falling forever in a daydream.

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It seems like a bit of a ridiculous concept. I mean, how could you possibly just fall forever?

Even if you could just fall through the Earth you’d eventually reach the middle right? Sure, you might bounce around like a slinky for a while, but at one point or another it would all come to a stop.

But what if we could ignore these restrictions and somehow get this bottomless pit to loop back on itself?

It doesn’t seem possible if we’re falling in a straight line. How could something always falling in one particular direction end up in the same spot over and over again?

Well the International Space Station does just that.

Orbiting the Earth at about 400km, it’s constantly free falling toward the Earth. That’s almost 1000 times closer to us than the moon which clearly experiences Earth’s gravitational pull. And yet, somehow the great satellite stays up there.

 

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But how exactly does that make sense? Why doesn’t it just plummet into a fiery wreck if all it does is fall toward the Earth from gravity?

In short: because it’s going really fast. Almost 8km per second fast. That’s about 288 times what you’d do on a free way in Melbourne.

Let’s take a step back.

Imagine dropping a ball from high in the air. Subject to gravity, you’d expect it to just fall to the Earth.

What if you threw it parallel to the Earth? Sure it’ll travel some distance over a map, but the end result will still be the same. That ball’s going to land somewhere on the Earth.

That is, unless you threw it unbelievably hard. Imagine the ball travelling so quickly that as it fell from the sky, the Earth curved away at the same rate!

Throw it too hard and it’s not coming back down. Get the speed right however, and it will maintain a constant distance from the ground, essentially orbiting our planet.

Granted we’re making some pretty serious assumptions here, ignoring things like wind resistance and putting enough force into an object to obliterate it.

But what about in space though? Can we ignore the limitations of Earth’s atmosphere?

In essence, what the ISS experiences is an ‘endless falling’ toward the Earth. As quickly as it falls, the Earth curves away! A bottomless pit!

That weightlessness or ‘zero gravity’ you see from videos of astronauts floating is in actuality a kind of falling toward the Earth.

The ISS and astronauts inside and attached to it are both falling at the same rate. Relative to each other, neither is moving and thus we perceive it as floating.

This isn’t unique to satellites or the moon. One could also see the Earth and other planets as falling toward our sun!

Next time you’re floating in a pool, consider that perhaps you’re actually just falling into the centre of our solar system – along with the rest of us!

References

NASA, April 11, 2016, About the Space Station: Facts and Figures. [ONLINE] Available at: https://www.nasa.gov/mission_pages/station/main/onthestation/facts_and_figures.html [Accessed 8 May 2016]

 

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This entry was posted on April 15, 2016 by in Uncategorized.

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