Brain Teasers

Orbiting is within the effective distance of the earth where gravity still affects an object. Once you get far enough away, there is little effect from the earth's gravity..

Greg L

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LsFarm wrote:Orbiting is within the effective distance of the earth where gravity still affects an object. Once you get far enough away, there is little effect from the earth's gravity..

I'm not being a wise guy here Greg but doesn't Earth's gravitational effect extend a pretty fair distance into space & isn't the moon captured & forced to orbit the Earth due to the huge gravitational effect of the Earth all the way out to the Moon & far beyond?
If so, then why are the Astronauts weightless traveling to & from the moon? Shouldn't they have "some" weight, albeit reduced due to distance?
and
If it's a matter of a reduction in Earth's gravity due to distance, is there a distance from the Earth at which gravity just comes to a screeching halt?

Edit: Obviously open to anyone but would love to hear from any engineers up on this kind of stuff

Devil505 wrote:So, why are astronauts still weightless in their spacecraft when they are not falling around the Earth? (say when they are going to or from the Moon)

I layman terms they are not weightless but the solar system objects pulling on them are far, far away, producing little pull. Our moon is small compared to earth so it's pull on Astronauts on it is much less than the pull on them on earth. It obviously was enough to keep them on the lunar surface.

Yanche wrote:I layman terms they are not weightless but the solar system objects pulling on them are far, far away, producing little pull.

Thanks for the input Yanche but I don't think the astronaut's apparent weightlessness on their way to or from the Earth is a matter of distance for the reasons I mentioned above. (Earth's gravity is still powerful enough to keep a huge mass like the Moon orbiting the Earth at quite a distance, so the "Moon Bound" astronauts are still well within Earth's powerful gravity. So, why are they apparently weightless????

Edit: Let me belabor the subject a bit more:
On all of our moon shots (Apollo) The 3 astronauts first orbit the Earth a few times to configure the Apollo capsule & the LEM (Lunar Excursion Module) in the nose to nose configuration they will need to goto the moon. At some point, a "burn" is initiated (TLI...Trans Lunar Insertion burn) that breaks the capsule away from eEarth orbit & heads them off to the Moon. During this TLI burn, the astronauts are again pressed back into their seats due to the engine's thrust.

BUT

As soon as these engines shut down, while the capsules are still close to the Earth but no longer in orbit & on their way to the Moon...The astronauts are again (immediately) apparently totally weightless .
Why???

You answered your own question, the earths gravity can affect a large object like the moon but has little effect on a small object like the space capsule and the astronauts..

The sun pulls on the planets and keeps them in orbit, but has little effect on men on Earths surface, otherwise you would weigh more at night when the sun is on the other side of the earth. or less at noon when the sun is overhead.

It's a matter of mass and distance.. I can't remember my physic anymore, but have the gist of it in general terms.

Greg L.

Because only the totality of the solar system is pulling on them. Do a search on "what holds the universe together" for a lot of info. While it's true any planet's moon is held in place by that's planet's gravitational forces, it only a part of the force, our sun being the major force keeping it all together.

LsFarm wrote:You answered your own question, the earths gravity can affect a large object like the moon but has little effect on a small object like the space capsule and the astronauts..

Maybe it's because it's been a long day & I am tired Greg but I still can't get my brain wrapped around your explanation. I could buy it better if the moon bound astronauts weight was reduced the further they got from the Earth......But totally weightless even in close proximity to the Earth but no longer in orbit????

I think it has more to do with the relationship between the astronauts & their spacecraft, both traveling at the same speed & therefore the apparent weightlessness of the astronauts within their capsule than it does with their mass & distance to the Earth. (sort of like a man in a falling elevator that will never reach the ground is still firmly in a gravity field but is weightless in relation to the elevator cab)
Have a germ of an idea but can't solidify it!

Belabor # 2


OK......thinking about it more, I think the "falling" part is the key. Both the astronauts & the spacecraft are in free fall, but what the hell are they falling into/towards on their way to the moon when they are no longer falling around the Earth in orbit??

gravity on earth and in the solar system and beyond , is one of the biggest mysterys that will always be unsolved.

ken wrote:gravity on earth and in the solar system and beyond , is one of the biggest mysterys that will always be unsolved.

You are right Ken. While we know its effects & can measure it very accurately, I don't think any scientist has ever been able to explain why masses attract each other???
But, we don't need to be able to explain what it is to answer my question though. We just have to explain the "why weightless on the way to the Moon & back", which is a purely measurement question.

(after I figure this out I will divulge what happens to us after death! ......which everyone know is that your sole goes to a vacant garage in Cleveland, according to the late George Carlin!)

Newton defined gravity quite well with his universal gravity equations. The force of gravity is dependent upon the mass of the bodies and the distance between the bodies. Thats why the apparent weightlessness of space flight. A spacecraft is indeed falling toward the body it is attracted to provided is is not exceeding the excape velosity of that body. Objects in near earth proximinity stay there because of the balancing act between gravity and the centrifical force (escape velocity) created by their orbit. To return from orbit a spacecraft is slowed down so that once again gravity is the stronger force.

http://www.school-for-champions.com/sci ... uation.htm

Steve.N wrote:A spacecraft is indeed falling toward the body it is attracted to provided is is not exceeding the excape velosity of that body.

OK......So let me try to think this through & my strictly layman's and amateur way.

As I understand it, when an Apollo spacecraft fires it TLI burn (& is thus traveling fast enough to escape Earth's gravity & head away towards the moon) it (spacecraft) can be thought of as climbing uphill, away from the Earth, & the spacecraft's "upward" velocity will be gradually slowed by the Earth pull (gravity) all the way to the Moon.......UNITL the spacecraft gets close enough to the moon to fall within the Moon's gravity, at which point it begins "falling" towards the Moon.
How my doing so far?

That is the way I understood it from advanced physics so long ago. As I recall to get away from earth gravity you need a velocity of around 11 KPS, obtain that and you don't come back. When you made the example of the 200 pound guy jumping off the scale he was generating vertical velocity. If you read the scale at the instant of liftoff it would have read somewhat more than 200 pounds causing him to overcome gravity for an instant. Of course his velocity is small in relation to gravity and he falls back.

According to Newton everything generates gravity including you and I, the denser the object the higher the gravitational pull. Even though the Earths gravity is strong compared to the moon the moon still effects our ocean tides

Steve.N wrote:According to Newton everything generates gravity including you and I, the denser the object the higher the gravitational pull. Even though the Earths gravity is strong compared to the moon the moon still effects our ocean tides

OK Steve, getting back to my "Uphill" analogy above..........If the Apollo astronauts are, in effect, climbing uphill away from the earth, then they are not "falling" so why are they apparently weightless in their capsule?