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h'd scr'tch - - say what?
If you're referring to the oscillating astronauts, then what was meant was that regardless of size, one object orbiting another is actually two objects swinging around their common center of mass. A huge object like a planet orbited by relatively tiny objects like a typical moon isn't affected much. It may have ocean or atmospheric tides created by the moon on the surface of the planet but the planet doesn't get displaced in space very much at all. However, two objects of the same size are each affected equally and rotate around each other like a weightlifters dumbbell flying through space.
A planet and small moon has the center of mass somewhere off center of the middle of the planet, but still inside the planet. To an observer out in space watching the pair, the heavier object hardly wobbles at all
Two equally sized planets orbiting each other have their center of mass in the middle of the space between the two planets. To an observer out in space watching the pair, the two objects wobble considerably.
Stars and their planets are in the first class.
Jupiter and its moons are in the first class.
Even the Earth and its moon are in the first class.
But Pluto and its relatively large moon Charon are in the second class.
Binary stars are often in the second class.
Neighboring galaxies are often in the second class.
However, if you were asking "say what?" because you're totally confused by the long winded amateur discussions of orbital mechanics and the nature of reality then don't let it bother you unless you plan on visiting a space station and dropping a bowling ball on your feet while traveling at the speed of light! Just don't fly on "Virgin Galactic" spaceliners. 8-o
Perhaps this will help a little... Centripetal Force on board the International Space Station > https://www.youtube.com/watch?v=A7WJ9FPEYU4
Note how the bungee cord in the video is being pulled on by the tool rotating around it. This is related to the oscillation mentioned by Richard and Rashad. If an astronaut held the spinning tool instead of the bungee cord holding it then the astronaut would be affected in a similar fashion and pulled on by the motion of the tool. Thus the astronaut might develop an oscillating motion under the spinning pull of the tool.... Not sure I'm explaining this very well.
Edit: Here is a longer and more informative version of the above video... https://www.youtube.com/watch?v=bYqXyEJb4vI
No, the laws of physics are the same on Earth, in space, and in your living room, so no separate test in space is needed.
All you need to check the theory is some string and a weight to put on the end of it. To make precise measurements of the effects needs more equipment, but any decent high school physics lab can do all the measurements needed to allow an engineer calculate the rotation speeds required. Of course they don't need that data because the measurements were done long before any of us were born and the theory has been tested over and over since then.
No, the laws of physics are the same on Earth, in space, and in your living room, so no separate test in space is needed.
All you need to check the theory is some string and a weight to put on the end of it. To make precise measurements of the effects needs more equipment, but any decent high school physics lab can do all the measurements needed to allow an engineer calculate the rotation speeds required. Of course they don't need that data because the measurements were done long before any of us were born and the theory has been tested over and over since then.
Best answer yet!
Best answer yet!
Best answer yet to the specific question quoted by Fire Angel? ...Perhaps. ...It certainly is correct!
Not, however, what I would consider the best answer to the thread in general. It answers a question but does not provide any type of deep understanding of the question or its answer, and therefore may fail to truly educate. ...Just my two cents worth. (Makes me wish I had Richard Feynman's knowledge and skill as an educator.... Unless Misty is just having a lark with us. ...No harm or bad feelings intended.)
If you were an an astronaut on a space station without artificial gravity, you could still do pushups to keep in shape. Anchor your feet to a deck, wall, whatever. Grab hold of a large weight, roughly half your body mass. Now push the weight back and forth vigorously with your arms. When you push, your body moves away from the center of gravity, and the weight moves away from it in the opposite direction. When you pull, this is reversed. By pushing and pulling vigorously, you are creating momentum, then absorbing and reversing momentum, thus exercising your muscles. The ISS has a treadmill and a stationary bicycle.
I forget which mission it was, but I believe there was a Russian Cosmonaut who spent so long in space, he could not stand up when he came back to earth, because his leg muscles had lost so much muscle tone from being weightless. It took him a while to recover.
More interesting articles:
http://en.wikipedia.org/wiki/Weightlessness
http://en.wikipedia.org/wiki/Effect_of_spaceflight_on_the_human_body
http://en.wikipedia.org/wiki/Artificial_gravity
Yes, the chief reason none of the proposed schemes for artificial gravity has been built is purely cost. The physics is sound, the engineering is not that complex, but the sheer cost of putting that much material in space is prohibitive.
On a mission to Mars, you could have a craft with a living quarter module and a rocket motor module. Once on the way to Mars, assuming no major course corrections are needed, the rocket motors would be off. The living module could be separated from the motor unit. The living module could be tethered to the motor by a long steel cable and they would spin around each other like a Bola. At a 224 meter radius and 2 RPM, the astronauts would feel quite comfortable. Shortly before arrival, they would have to stop the rotation and rejoin with the motor unit for deceleration into Mars orbit. They have performed tether experiments in space, but not on a large scale, which is when we come back to the cost issue. The Tempo3 project never happened.
This is the system Zubrin came up with for his Mars Direct mission concept. It looks a bit ridiculous, but there's nothing too complicated about the engineering; it should Just Work™ with no major surprises.