WootBot


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As NASA’s Curiosity rover continues to inch across the red planet’s dusty Gale Crater, America’s interest in space exploration inches upward as well. Jeopardy!’s Ken Jennings is a bit of space nerd himself, and this month he’ll be navigating us through an asteroid belt of misconceptions about the exploration of the cosmos. Even if you’re not one of the 6 percent of Americans who believes that the moon landing was a hoax, you might have been fleeced by one or more of these fallacies about the final frontier.

Space Myth #3: Astronauts Are Weightless in Space Because They’re Beyond Earth’s Gravity.

We’ve all seen the images of astronauts—real-life and movie ones alike—bouncing around the insides of their space capsules like crewcutted Ping-Pong balls. Of course, we think. On Earth, there’s gravity. In space, far from the Earth’s pull, there’s not. But that’s not even close to correct.

Remember that gravity is one of the fundamental forces of the universe, so it’s everywhere. According to Newton’s laws, it diminishes fairly rapidly with distance, but objects in low Earth orbit, like a Space Shuttle, are only 350 kilometers or so above the planet—the Moon is over one thousand times farther away! If you do some rough math, you’ll see that the gravitational force on an astronaut in orbit is still about 650 newtons, about 90% of what it is on Earth. Gravity is almost identical in orbit! So how are spacemen doing those cool tricks with the spinning clipboards and the floating Tang and whatnot?

An astronaut in orbit feels weightless for the same reason a skydiver does: he’s falling. Or, to be precise, his spacecraft is falling, and he’s falling inside it at exactly the same speed. You could get the exact same experience (more briefly) inside a free-falling elevator—and you could do all his cool bouncing-off-the-ceiling space tricks in a falling elevator, like Joseph Gordon-Levitt in Inception. The spacecraft is falling, but it doesn’t fall to Earth. Why? Because it’s moving forward sufficiently fast (17,500 miles per hour, aka “orbital velocity”) that as it falls, it falls around the Earth. And keeps falling, making a near-circular orbit, until it slows down enough (using its engines, in the Space Shuttle’s case) to leave orbit in a controlled way and return to Earth.

Without gravity, none of this would be possible. Of course, it’s also possible to imagine an astronaut somewhere in deep space, too far from any celestial body for anything to pull noticeably on him. Now that guy has the exact same weightless feeling he would in orbit, but in his case it is due to a lack of gravitation. Unfortunately, he’s probably dead.

Quick Quiz: What musician’s hit song “Living in America,” featured on the Rocky IV soundtrack, appeared on his 1986 album Gravity?

Ken Jennings is the author of Because I Said So!, Brainiac, Ken Jennings's Trivia Almanac, and Maphead. He's also the proud owner of an underwhelming Bag o' Crap. Follow him at ken-jennings.com or on Twitter as @KenJennings.

StanleyS


quality posts: 5 Private Messages StanleyS

"Lack of gravitation"? I can't find my Physics 1 textbook at the moment but "gravitational attraction - the force of attraction between all masses in the universe". ALL masses! Meaning that there is a gravitational attaction between an atom in front of me and an atom a billion light years away. Not much attraction, but not zero attraction. I think Ken means "little" rather than "lack".

Bud Ward


quality posts: 0 Private Messages Bud Ward

Surely you meant "orbital velocity". "Escape velocity" is over 25,000 MPH.

BorisBadenov


quality posts: 0 Private Messages BorisBadenov

Gravity in space is like the balance of my bank account. It is non-zero, but the effect it has on the rest of the universe is so small as to make no practical difference.

tslothrop


quality posts: 12 Private Messages tslothrop

Orbital velocity varies with the height of the orbit, it is not a fixed number. The elevator analogy is flawed as well, as there is no such thing on earth as a free-falling elevator.

john27


quality posts: 4 Private Messages john27
tslothrop wrote:Orbital velocity varies with the height of the orbit, it is not a fixed number. The elevator analogy is flawed as well, as there is no such thing on earth as a free-falling elevator.



A free falling elevator could happen briefly if it's cables became cut!

A better analogy would have been what was used to film Apollo 13, or is used to help astronauts train; a large aircraft that flies to a high altitude, then goes into a controlled 0G dive (diving at just the right speed and angle to create 'free fall'). They can do all the same cool spinny tricks for about 2 minutes or so. There's a scene in Apollo 13 if you look carefully, where a roll of floating duct tape suddenly jolts to one side, then the camera cuts. That's because the plane was beginning to pull out of the controlled dive. Unlike a spacecraft in orbit, an airplane isn't flying near fast enough to remain in freefall forever, AND, is still within the atmosphere so it won't be able to reach those speeds. (The reason we orbit in space is not because of gravity, it's because of the atmosphere, no wind resistance!)

Another fun fact, although when speaking to the public they'll often use the misnomer 'zero gravity', Astronauts typically use the term 'free fall' to describe the weightlessness. Because that's exactly what's happening, they are in a free fall. Although, as long as the orbital trajectory isn't ever placed back in the atmosphere where it'll be slowed down, they'll be freefalling indefinitely.

Obviously you're right about orbital velocity varying. However, save for certain communications, GPS and spy sattelites (often in sun synchronous or geostationary orbits which are much higher), we haven't left low earth orbit since the last moon landing (manned anyway), and the vast vast majority of our orbiting spacecraft fly at an altitude of 2,000km and a velocity of 17,500mph

dukeofwulf


quality posts: 7 Private Messages dukeofwulf

"James Brown"

Since no one else was going to say it...

jcolag


quality posts: 8 Private Messages jcolag

Are there people who actually believe this? Of them, how many are able and permitted to use a computer?

I feel like every cartoon, science fiction, and even remotely space-related show ever has brought this up at least once to correct any misconceptions that might have arisen in the twenty minutes since the last explanation.

Still, no discussion of the topic is complete without the Heavy Boots discussion. (The "six to seven years" was old when I was in college in the '90s, in case anybody wants to try to hunt backward for a source.)

metagg


quality posts: 1 Private Messages metagg

Looks like somebody graduated from the second grade.

Jason Toon


quality posts: 19 Private Messages Jason Toon
jcolag wrote:Are there people who actually believe this? Of them, how many are able and permitted to use a computer?



metagg wrote:Looks like somebody graduated from the second grade.



I think you guys vaaaaaaaastly overestimate the scientific literacy of the average computer user and/or second-grade graduate.

StanleyS


quality posts: 5 Private Messages StanleyS
Jason Toon wrote:I think you guys vaaaaaaaastly overestimate the scientific literacy of the average computer user and/or second-grade graduate.


The clock on my VCR keeps blinking "12:00". Can you tell me how to fix it. In simple terms. I can't be bothered reading the manual.

wisenekt


quality posts: 29 Private Messages wisenekt
StanleyS wrote:The clock on my VCR keeps blinking "12:00". Can you tell me how to fix it. In simple terms. I can't be bothered reading the manual.



Simple fix, throw out the VCR. It is far outdated technology.

StanleyS


quality posts: 5 Private Messages StanleyS
wisenekt wrote:Simple fix, throw out the VCR. It is far outdated technology.


How am I going to play my Jane Fonda Workout tape, then?

whoiskenjennings


quality posts: 7 Private Messages whoiskenjennings

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Yeah, "escape velocity" is totally wrong, oops. Should say orbital velocity. Sorry about that! No idea what happened there.

ringstad


quality posts: 0 Private Messages ringstad

Skydivers don't feel weightless.

jai151


quality posts: 8 Private Messages jai151
ringstad wrote:Skydivers don't feel weightless.



They also have a frame of reference and wind. If you made an opaque shell around them, they would feel weightless.

Well, until they hit ground, anyway.

Bud Ward


quality posts: 0 Private Messages Bud Ward
jai151 wrote:They also have a frame of reference and wind. If you made an opaque shell around them, they would feel weightless.

Well, until they hit ground, anyway.



No, once they reach terminal velocity they are no longer in free fall.

thurin


quality posts: 5 Private Messages thurin

put a piece of duct tape over it.

bacalum


quality posts: 4 Private Messages bacalum

I love gravity. I pour lots of it on Thanksgiving turkey and mashed potatoes.

When rich or powerful people propose a change, it is designed to make them richer or more powerful.