astronauts, misconceptions, and google

[mediawest]

Why are astronauts weightless when they're orbiting around the planet in their space shuttles? Obviously, it's because outer space is a zero-gravity environment. Right? Are you sure?

Let's use Google to double-check. Try cutting and pasting this formula into google:

(G * mass of earth)(70kg) / ((70kg)*(radius of earth ^ 2))

Pretty neat, huh? Google has just calculated the approximate gravitational acceleration on an astronaut-sized object on the Earth's surface. Now, the spaceship can reach orbits up to about 650km above the Earth, so try adding the additional distance to the earth's radius: you can augment the formula by replacing "radius of earth" with "(radius of earth+650km)".

Did the additional distance cause the gravitational acceleration to attain a near-zero value? Are the astronauts really in a near-zero-gravity environment? And more importantly, is there anything that Google doesn't know how to do?


The preceding exercise seems to take many adults by surprise. It turns out that astronauts are weightless not because they are floating in space, but because they are falling in space.

[Jinto]

First, welcome to IIDB.

Second... we already knew this.

[wade-w]

Do ya think maybe that's why it's called free-fall?

[Jackalope]

Yes, however you'd be suprised how many adults out there still think that "zero G" and "freefall" are synonyms for "weightless." The idea of continually falling around an object (well, duh, that's what an orbit is) seems to jam a lot of people's mental gears. Which is why most people use the analogy of an endless elevator ride down to explain it to the scientifically challenged. An elevator going down is something they've experienced before.

Even more fun is trying to explain the real effects of hard vacuum on living beings. (No, they don't explode)

[viscousmemories]

Sheesh, tough crowd. Person uses his/her first ever post here to say, "Google is a cool resource and here's a fun science fact I learned that many people may not know", and gets "No shit, Sherlock" in response. What's up with that?

vm

[Demosthenes]

That reminds me of a time on amazon.com when I was reading reviews of a scifi movie. In the movie, a character is exposed to hard vacuum and suffers only few side effects which included not exploding. There was a review where a guy claimed to have advanced scientific knowledge and in the same breath, he said that the character SHOULD have exploded because "everybody knows that in vacuum people blow up" :rolleyes: What a dimwit.

[livius drusus]

Originally posted by viscousmemories
Sheesh, tough crowd. Person uses his/her first ever post here to say, "Google is a cool resource and here's a fun science fact I learned that many people may not know", and gets "No shit, Sherlock" in response. What's up with that?

Amen, brother. The OP was all news to this English and History major and I found it quite charming. Don't let these curmudgeons buzzkill you, mediawest. Welcome to IIDB.

[Friar Bellows]

Originally posted by mediawest
Let's use Google to double-check. Try cutting and pasting this formula into google:

(G * mass of earth)(70kg) / ((70kg)*(radius of earth ^ 2))

What a nifty feature! Thanks for letting us know.

[Artemus]

My high school physics teacher told us that weightlessness occurred due our bodies own gravity attracting the walls of the spacecraft equally. The poor man tried very hard, but he had quite a few of these type misconceptions that he passed along.

[Worldtraveller]

First of all, welcome to IIBD mediawest!

And remember, you don't actually need to be in orbit/outer space to experience microgravity (the proper term).
My dad is a pilot, and took me flying with him in some high performance aircraft more than once. In his many efforts to try and induce motion sickness in me (yeah, my dad, like most, is a sadistic bastard! :) Luv ya dad!!) used several thousand feet of altitude in a nice smooth parabolic curve simulating zero g.
I even let a pen float in front of my face for a good 8-10 seconds to see the effects. It was very cool. :D
Been there, done that.


Cheers,
Lane

[nermal]

Originally posted by Artemus
My high school physics teacher told us that weightlessness occurred due our bodies own gravity attracting the walls of the spacecraft equally. The poor man tried very hard, but he had quite a few of these type misconceptions that he passed along.

Ah, but there is a point where that would be true. What if the ship were in a fixed orbit, and you step off toward earth. There would be some distance from the earth where the close proximity of the ship balances the gravity of the earth. I bet it ain't that far away either, when you consider how minutely you are inside the orbit radius for your velocity. Betcha the google thing could calculate that too.

:cool:

Ed

[Calzaer]

Even more fun is trying to explain the real effects of hard vacuum on living beings. (No, they don't explode)

Oooh! Oooh! Tell me! What happens??

[butswana]

suffocation

[tribalbeeyatch]

Originally posted by butswana
suffocation Is that all? Wouldn't their lungs explode and the blood gases bubble like with the bends?

[Kat_Somm_Faen]

Ok so in vacuum we have total lack of pressure and temperature also, true? In essence one would be completely isolated and only means of temperature rise or drop would be radiating heat in or out of you.

If I am correct, gas is contained in fluid by means of pressure of the gas on the surface above the fluid. So boliling would not be due to temperature but teh gas contained in teh blood and lungs start being forced out. So not really boiling that we have in mind but something else. Also explosion would not happen but our bodies would still tend to expand since we have a certain amount of internal pressure. The air in our blood and lungs would expand. Similar thing happens with weather ballons. As they rise they pressure drops and the volume contained within the baloon expands making it bigger. In essence you would baloon like a michelin man, you veins and arteries also balooning, the gas disolved in your blood would fizz ( or whatever ) out of you while your brain might still be alive and recording everything. Vessels would burst and you would be oozing and gushing blood out of every orifice and some new ones at least until your blood pressure drops and/or heart stops.

Now take it easy on me with criticism! :D

....

Edit: The gas dissolved in water is known to everyone by a fizz of a soda or mineral water. In essence those are molecules of CO2 disolved in water and once the pressure is lowered by opening the bottle the gas is being expelled out of the water into the atmosphere. So your blood should fizz until most of the dissolved gas is out. Chemically bonded oxygen and other gasses should be a different story.

[tribalbeeyatch]

Also, wouldn't the internal pressure of each of the cells that constitute the body cause them to rupture? What might that look like?

[Kat_Somm_Faen]

I am not sure what is the internal pressure a property of.

If it is a property of individual cells or mucle contraction around the fluid filled sacks that are muscles or what. Anybody here a biology major?

In essence a small tear would be enough to equate the pressure. It does not need to be a consequence of some pop of the entire cell. Just like the tire need aonly a small hole to even out the pressure it does not have to be catastrophic failure.

IMO depends on what makes up our internal pressure. And I dunno.

[tribalbeeyatch]

It's osmotic pressure that's maintained by regulating the salt balance inside the cells, if I'm not mistaken. You're probably right, though, that it wouldn't be a 'pop' since the phospholipid bilayer is somewhat self-repairing, but I would imagine that a lot of cytoplasm would be released before the pressure dissipated. Maybe the skin and exterior anatomy (e.g. eyeballs...ewwww) would just get slimy and flaccid?

[Artemus]

Originally posted by nermal
Ah, but there is a point where that would be true. What if the ship were in a fixed orbit, and you step off toward earth. There would be some distance from the earth where the close proximity of the ship balances the gravity of the earth. I bet it ain't that far away either, when you consider how minutely you are inside the orbit radius for your velocity. Betcha the google thing could calculate that too.

:cool:

Ed

You would need to be a long, long way from the Earth for this to be true. The inverse square law applies as the distance from the center of mass (approximately...exactly for a uniform sphere), so you will always be a number of feet away from the ship gravitational center. As the mass of the ship is trivial compared to the Earth's, you can see that it will be a *long* way despite the square root.

He also told us that resistors in a circuit heat up due to destruction of electrons. *sigh*

[nermal]

Originally posted by Artemus
You would need to be a long, long way from the Earth for this to be true. The inverse square law applies as the distance from the center of mass (approximately...exactly for a uniform sphere), so you will always be a number of feet away from the ship gravitational center. As the mass of the ship is trivial compared to the Earth's, you can see that it will be a *long* way despite the square root.

He also told us that resistors in a circuit heat up due to destruction of electrons. *sigh*

Make no mistake, I'm not defending your teacher's position. He was wrong, pure and simple. However:
I don't think you're taking into account the orbital velocity of the astronaut, relative to the earth. He is only a few meters inside a stable, or "weightless" orbit (the ship's orbit). The force vectors acting on him are:
1. Earth's gravity
2. The acceleration of his orbit acting against earth's gravity
3. The ship's gravity.

2 and 3 combined must counteract 1. 2 is nearly equal in magnitude to 1. Therefore, 3 needn't be that significant. I don't think you would have to be as far from earth as you think.

Ed

[Shadowy Man]

Originally posted by nermal
I don't think you're taking into account the orbital velocity of the astronaut, relative to the earth. He is only a few meters inside a stable, or "weightless" orbit (the ship's orbit). The force vectors acting on him are:
1. Earth's gravity
2. The acceleration of his orbit acting against earth's gravity
3. The ship's gravity.

2 and 3 combined must counteract 1. 2 is nearly equal in magnitude to 1. Therefore, 3 needn't be that significant. I don't think you would have to be as far from earth as you think.

I'm not exactly sure what you are getting at here, but you can calculate the force on the astronaut by the Earth, and the force on the astronaut by the spacecraft.

Because the astronaut is inside the spacecraft, much of the gravitational force on him by the craft will cancel out (i.e. the mass of the craft to the left of him will pull him in one direction, but the mass on the right will pull him in the opposite direction).

Being in orbit, he is essentially falling freely toward the Earth. The spacecraft is falling with him, so relative to the craft it is as if there were no gravity at all. He could hold a pen out next to him, and when he lets go it wouldn't fall down from his hand because they are actually both falling, and at the same rate.

[Jesse]

Originally posted by nermal
Make no mistake, I'm not defending your teacher's position. He was wrong, pure and simple. However:
I don't think you're taking into account the orbital velocity of the astronaut, relative to the earth. He is only a few meters inside a stable, or "weightless" orbit (the ship's orbit). The force vectors acting on him are:
1. Earth's gravity
2. The acceleration of his orbit acting against earth's gravity
3. The ship's gravity.

2 and 3 combined must counteract 1. 2 is nearly equal in magnitude to 1. Therefore, 3 needn't be that significant. I don't think you would have to be as far from earth as you think.

Ed

#2 is a fictitious force, a consequence of looking at the situation from within an accelerated reference frame. And in free fall #2 should counteract #1 exactly--for any system falling freely in a gravitational field, the fictitious force pointing up due to downward acceleration is equal in magnitude to the gravitational force pointing down, so that within this accelerated reference frame there appears to be no net force on the system (weightlessness).

[nermal]

Originally posted by Shadowy Man
I'm not exactly sure what you are getting at here, but you can calculate the force on the astronaut by the Earth, and the force on the astronaut by the spacecraft.

Because the astronaut is inside the spacecraft, much of the gravitational force on him by the craft will cancel out (i.e. the mass of the craft to the left of him will pull him in one direction, but the mass on the right will pull him in the opposite direction).

Being in orbit, he is essentially falling freely toward the Earth. The spacecraft is falling with him, so relative to the craft it is as if there were no gravity at all. He could hold a pen out next to him, and when he lets go it wouldn't fall down from his hand because they are actually both falling, and at the same rate.

Read the previous posts.

Ed

[Jackalope]

Skin's a lot tougher than most people give it credit. So no, no exploding. Yes, the alveoli in the lungs would rupture. Probably not the cornea of the eye, as it's also quite tough. However, the small blood vessels in the eye do rupture. Plus, you get the moisture on the eye turning to ice and sublimating as well. Gotta hurt.

So yes, bleeding out the mouth and nose, especially since the lungs are taking damage. Bleeding in the eyeball, frozen corneas. Lots and lots of broken blood vessels. And suffocation. If one lived longer without oxygen, one might develop the bends as gasses bubbled out of solution in the blood. End result: a freeze-dried corpse, but still all in one piece.

[andy_d]

How quickly you decompressed would also come into play. Obviously the faster you decompress, the less fun it will be.

For a practical demonstration of why space suits are recommended attire for spacewalks, rent the movie "Event Horizon" ;)