Need help generating gravity

[Aliasalpha]

For a story that is. I'm writing a short story set on mars and I want a gravity generator that works inside the domed cities so I don't have to deal with low gravity conditions. I plan to have a scene or 2 outside the domes so I can use low gravity conditions but for the majority I want near earth gravity.

Effectively want I want is magic that works only in the domes, I don't need anything super technical since I plan to gloss over it but I'd like something that's not totally implausible.

[fafalone]

Well it would be relatively simple (and scientifically plausible) to use superdense matter (i.e. from a collapsed star, or more likely since its on Mars a new method for collapsing matter) buried reasonably far under the surface to increase the gravity...

[Crash]

A sorta mini-black hole for finctional purposes just enough to supply HUGE gravity without crushing anything

[fafalone]

Dense enough to be a black hole is a really bad idea... matter can be dense enough to create a gravity field without being a black hole.

[Crash]

well.this is fictional dosent have to be plauseable....

"I don't need anything super technical since I plan to gloss over it but I'd like something that's not totally implausible"
yea i guess i like the superdense material one the best......it leaves alot for the imagination

[Aliasalpha]

Well I'd prefer it to be plausible, the only thing I'd thought of is some kind of undreground rotating ,echanism or superdense matter

[Pinch Paxton]

Underground rotation wouldn't work. The dense material would work. The black hole would destroy Mars.

[Radical Edward]

I would go for the superdense matter thing. Or even forget about it altogether like Cowboy Bebop or Total Recall do.... but then why not just have low G on mars?

[YT2095]

yeah, super dense seems the way to go.
but since it`s fiction" and I`m not certain if mars has magentic poles or not, but another idea to play with might be a huge super conducting magnet in the core using the polar ice caps for the "chill factor" and each resident on mars takes a shot of a ferro-magnetic alloy that binds to cellular proteins and simulates gravity by magnetic pull, that way you can play about with the idea off worlders that havent has that shot and have seemingly super human strength and all manor of adventures can take place from there :)


hey, it`s just a few ideas :)

[alt_f13]

No, check this. Race track style rotating surface. That way the gravity is increased but nobody can go in the middleof the domes, just the portions that are tipped upwards. Mars' natural gravity and centripital force would work together in this case and the physics have already been proven on car test tracks.

OTHERWISE

Have a series of particle accellerators underneath the domes. These extremely advanced accellerators would be used to send streams of Tritium (the heaviest of the hydrogen isotopes... it doesnt really matter.. the point is its HEAVY and tritium sounds good) in circles under the domes. With the tritium reaching near light speeds it would create strong gravitational fields because of the density of the atoms becoming greater.

This way you could add or subtract particles to adjust the ammount of gravity or have part of the accellerator become destroyed so only a small portion loses the gravitational pull.

[YT2095]

"No, check this."

what do you mean "NO"?, it`s F-I-C-T-I-O-N !!! LOL sheesh! :)

[iglak]

alt_f13 said in post # (http://www.scienceforums.net/forums/showthread.php?s=&postid=40581#post40581):
With the tritium reaching near light speeds it would create strong gravitational fields because of the density of the atoms becoming greater.
gravity isn't related to density, only mass and distance. but, increased relative mass might affect gravity (i don't know). so this could still work.

[mooeypoo]

Erm, I just finished reading a fiction story that explains some of Einstein's theories..

Isn't the only way of generating TRUE gravity (without actually greating a huge planet) is by Acceleration?

... ?

[Crash]

yea well what if you speed up the speed of the mars orbit and make it gain gravity that way.......you would need some serious boost for this though.........it could be done by mars gettin pushed by a explosion like a supernova up its tail but that would through it of course and we only got one sun.........

[NSX]

iglak said in post # (http://www.scienceforums.net/forums/showthread.php?s=&postid=40614#post40614):

gravity isn't related to density, only mass and distance. but, increased relative mass might affect gravity (i don't know). so this could still work.

m :alpha: :rho:

[iglak]

NSX said in post # (http://www.scienceforums.net/forums/showthread.php?s=&postid=40636#post40636):
m :alpha: :rho:
i don't know what that means, can you explain?
i assume m is mass. :alpha: could be acceleration. i have no idea what :rho: could be though.
is this m X :alpha: X :rho: = strength of gravity?

[alt_f13]

YT2095 said in post # (http://www.scienceforums.net/forums/showthread.php?s=&postid=40583#post40583):
"No, check this."

what do you mean "NO"?, it`s F-I-C-T-I-O-N !!! LOL sheesh! :)

Heheh. "No" as in "wait a sec."

[Aliasalpha]

I think I might go with the superdense matter. Hmm, there's a thought, I was planning to make a pretty major city inside the domes so it'd have the skyscrapers regular cities have (I think I've just decided to call them Domescrapers though), would the gravity extend far enough to cover the top floors? It might make an interesting scene to have lower gravity on the top floors.

[YT2095]

it would be a little lower, but only by 1000`th of a gram or so. the same rules would apply there as they do on Earth if you went with super dense matter.
indeed you weigh a little less ontop of Mt Everest than you do at sea level, but you wouldn`t notice it :)

[Duke]

How exactly would you obtain this super dense matter?

[JaKiri]

iglak said in post # (http://www.scienceforums.net/forums/showthread.php?s=&postid=40641#post40641):

i don't know what that means, can you explain?
i assume m is mass. :alpha: could be acceleration. i have no idea what :rho: could be though.
is this m X :alpha: X :rho: = strength of gravity?

The alpha is a very crude version of the symbol meaning 'proportional to'.

Mass is proportional to density.

[Cheetah]

Duke said in post # (http://www.scienceforums.net/forums/showthread.php?s=&postid=40683#post40683):
How exactly would you obtain this super dense matter?

It's fiction. Use some kind of special fusion or compression mechanism to create very heavy materials. :-)

[rjbowlin]

A different idea may be to create a magnetic field beneath the city and have everyday things doped in a given percentage of metal, cups,boots clothing.
foods & drink would have to be accounted for. However g on mars is half of earths, and so wouldn't be like bouncing around on the moon. I would think it would be considerably more controlable. Perhaps diet and the like have been adjusted for life on mars. ex. water being kept in a gelatinus state.

[JaKiri]

rjbowlin said in post # (http://www.scienceforums.net/forums/showthread.php?s=&postid=40703#post40703):
A different idea may be to create a magnetic field beneath the city and have everyday things doped in a given percentage of metal, cups,boots clothing.
foods & drink would have to be accounted for. However g on mars is half of earths, and so wouldn't be like bouncing around on the moon. I would think it would be considerably more controlable. Perhaps diet and the like have been adjusted for life on mars. ex. water being kept in a gelatinus state.

More trouble than it's worth.

[Crash]

its irrelevant to the story, but you have to manufacture it in the spot you wanted it to remain(remember this is to increase the overall gravity of mars) so its safe to say you wouldnt walk up to a star and pocket the superdense matter
BTW what is the most dense stable matter at the moment

[iglak]

MrL_JaKiri said in post # (http://www.scienceforums.net/forums/showthread.php?s=&postid=40689#post40689):
The alpha is a very crude version of the symbol meaning 'proportional to'.

Mass is proportional to density.
ah, okay, that makes sense. thx

[JaKiri]

Crash said in post # (http://www.scienceforums.net/forums/showthread.php?s=&postid=40745#post40745):
its irrelevant to the story, but you have to manufacture it in the spot you wanted it to remain

Why? Why CAN'T we move it?

F=ma duder.

[greg1917]

i don't know what that means, can you explain?

Mass varies as density.

A material with a higher density will have a higher mass than the same volume of a less dense material.

Thus density affects gravity and is an important consideration.

[YT2095]

this might be a mad idea as it`s based on a guess. if Earth were to stop rotating (slowly of course) would we weigh more?
obviouly our masses would remain constant, but the velocity we rotate at may have a "lightening" effect due to centripetal force.
maybe stopping Mars` rotation or slowing it could allow it`s natural gravity to have a greater effect?

I don`t know the maths or even if it`ll work, it maybe complete bull$h!t, but it`s an idea :)

[Aliasalpha]

I'd have thought the rotation would increase our weight rather than decrease it.

Hmm, I've just come up with a zany scheme to lose weight!
Step 1: Halt earth...

[YT2095]

it would increase weight if you were inside it like in a ball and it was spinning.

if you stopped the roation, my guess is that it would do one of 2 things, you`de gain weight, or it would have no effect.
I don`t know enough to comment :)

[Atlantic]

Mars is quite close to earth gravity, so i wouldn't go that far :)

[alt_f13]

YT2095 said in post # (http://www.scienceforums.net/forums/showthread.php?s=&postid=40834#post40834):
it would increase weight if you were inside it like in a ball and it was spinning.

if you stopped the roation, my guess is that it would do one of 2 things, you`de gain weight, or it would have no effect.
I don`t know enough to comment :)

 

I did the math once.  You do gain weight but not much.. I'll do it again and edit the post.

 

[edit]

Aight, check it, yo.

 

Earth's radius = 6.38 * 10^6 m = Re

Centripital accelleration at the surface = 4* Pi ^2 * R / T^2 = Ac

Accelleration due to gravity at Earth's surface = G * M / R = 6.67 * 10^-11 * 5.98 * 10^24 / (6.38 * 10^6)^2

=9.79909

Seconds in a day = 24 * 60 ^ 2 = 8.64 * 10^4


SO...

Your weight because of the earth's rotation is:

Ag + Ac = Ay * my (Accelleration on you times your mass)

9.79909 - 4 * Pi^2 * 6.38 *10^6 / 86400^2 = Ay

9.79909 - 0.03374 = Ay

9.79909 - 0.03374 = 9.76535

 


So the force on you now is 9.76535 * your mass.

The force on you w/o the rotation of the earth is 9.79909 * your mass.

The difference is 0.03374 * your mass.

 


To find out what the weight difference is in pounds take 0.03374 * your mass in kg * 0.22481

Or if you only know your weight in pounds, take your weight in pounds * 4.4475 / 9.76535 to get your mass and do the line above.

 


(Yah, I know there is an easier way to do it in pounds w/o all the newton stuff but imperial is for dorks and I didn't want to do any more math.)

[Crash]

well MrL_JaKiri
if were talkin superdense matter here, superdense enough to considerably raise the gravity of mars then
F=(insert large # here)*acceleration, i take it then that 'F' stands for F**]<in heaps

[Aliasalpha]

Actually that's an interesting point for my story, If I have say 20 chunks of superdense matter with cities perched on top would that be enough to alter the rotation or orbit of mars? I didn't plan to have them at even intervals or anything, just on the nice flat areas so would that create an imbalance?

[YT2095]

I would esstimate that a mass large enough to create a "normal" Earth gravity under a city(s) wouls also make a "wobble" as the rotation would be eccentric as a result.
in effect, it would be a BAD idea even if it were possible. :(

[Pinch Paxton]

Your book is getting too detailed in my oppinion. I'm a writer too!

[JaKiri]

Crash said in post # (http://www.scienceforums.net/forums/showthread.php?s=&postid=40907#post40907):
well MrL_JaKiri
if were talkin superdense matter here, superdense enough to considerably raise the gravity of mars then
F=(insert large # here)*acceleration, i take it then that 'F' stands for F**]&lt;in heaps

No, a force of 1N would do it. Might take a long time, but it'd do it.

[JaKiri]

alt_f13 said in post # (http://www.scienceforums.net/forums/showthread.php?s=&postid=40901#post40901):
Your weight because of the earth's rotation is:

I don't see quite where this is going, or what it's meant to demonstrate.

[alt_f13]

YT2095 said in post # (http://www.scienceforums.net/forums/showthread.php?s=&amp;postid=40822#post40822):
this might be a mad idea as it`s based on a guess. if Earth were to stop rotating (slowly of course) would we weigh more?
obviouly our masses would remain constant, but the velocity we rotate at may have a "lightening" effect due to centripetal force.
maybe stopping Mars` rotation or slowing it could allow it`s natural gravity to have a greater effect?

I don`t know the maths or even if it`ll work, it maybe complete bull$h!t, but it`s an idea :)

&nbsp;

The point is I would weigh half a pound more if the Earth was not rotating.&nbsp; That is the effect of centripital force on a person on the surface of the Earth.&nbsp; Almost negligable.&nbsp;

&nbsp;

Seeing as Mars is smaller it would have more of an effect but certanly not 50%.

[Aliasalpha]

Pinch Paxton said in post # (http://www.scienceforums.net/forums/showthread.php?s=&postid=40955#post40955):
Your book is getting too detailed in my oppinion. I'm a writer too!

Oh I wasn't planning on using that in the story, it was just a though

[ski_power]

One question about gravity. In a ring planet(a la Halo), will it be possible for natural gravity to occur. And assuming that it's characteristics(ie mass, density, angular momentum etc) are identical to the earth, then how much g would it exert on us?

PS: Are you guys geniuses or what?

[YT2095]

by "in a ring planet" do you mean a normal planet with rings? like Saturn or Uranus?
I think such a planet would have an additional "tidal" effect, but be so tiny as to be hardly measurable without equpment, but certainly a ring around a planet would have a gravitational effect much in the same way as our moon does, but it would be less pronounced as the moon`s a single dense object and moves quite quickly, whereas a ring is almost a constant mass in average density (assuming no moons).

secondly, I personaly do not consider myself a Genius. I`m just a ME :)

[ski_power]

When I said ring planet, I actually meant a planet which is in the form of a ring. And it spins along it's diameter.

[Sayonara³]

Certainly a Halo would have a gravitational pull, assuming of course it has mass which the thing you're talking about invariably would.

How close it was to Earth's gravitational pull would depend on the ring's dimensions and density.

I'm not sure how to work it out exactly but it would probably have to be one fat (or deep) ring.

[YT2095]

When I said ring planet, I actually meant a planet which is in the form of a ring. And it spins along it's diameter.

I`ve never heard of such a beast in all honesty (not to say it couldn`t exist however if made of strong enough material)
speeding up the rotation of such a structure would indeed inrease the centripetal force and weight of the folks inside the diameter of this ring of course.
I do however fail to see HOW this effect may apply to Mars that has no such facility?

[Sayonara³]

I`ve never heard of such a beast in all honesty
It's like a Dyson Sphere, only it's a ribbon instead of a shell. Slightly more feasible ;)

[swansont]

Certainly a Halo would have a gravitational pull, assuming of course it has mass which the thing you're talking about invariably would.

How close it was to Earth's gravitational pull would depend on the ring's dimensions and density.

I'm not sure how to work it out exactly but it would probably have to be one fat (or deep) ring.

There would be no gravity on the inside of the ring. Assuming a uniform mass distribution, gravity depends on the mass inside of your radius. This is from Gauss's law (used also in electrostatics - if the ring were charged there would be no electric field inside, either)

Whatever pull there is from the mass below your feet, it is counterbalanced by all the mass elsewhere in the ring. The sideways pull cancels from symmetry, but the up/down cancels, too. Even though a lot of the ring is far away, there's a lot of it compared to what's below you.

[ski_power]

But wouldn't Centripetal Acceleration give us gravity on the inside part of the ring?

[ski_power]

But wouldn't Centripetal Acceleration give us gravity on the inside part of the ring? Assuming it is rotating along it's principal axis, ie perpendicular to the plane through the centre

[Sayonara³]

There would be no gravity on the inside of the ring. Assuming a uniform mass distribution, gravity depends on the mass inside of your radius. This is from Gauss's law (used also in electrostatics - if the ring were charged there would be no electric field inside, either)

Whatever pull there is from the mass below your feet, it is counterbalanced by all the mass elsewhere in the ring. The sideways pull cancels from symmetry, but the up/down cancels, too. Even though a lot of the ring is far away, there's a lot of it compared to what's below you.
A Halo is only any use if the living area assumes the same position in space as the average position of the surface of a planet that would be able to support life. IE - the ring needs to be approximately the same size and shape (although probably less of an elipse) as an "M-class" planet's orbit.

The assumption with these things (unlike the Dyson sphere, which requires technological workarounds nobody has explained yet) is that the ring rotates like an enormous bicycle wheel.

Would it ever get fast enough to keep people "pinned" to it, or would people eventually end up drifting into the sun?

[ski_power]

Would it ever get fast enough to keep people "pinned" to it, or would people eventually end up drifting into the sun?

Now that's a good thought. It sounds serious, but after a second look it sounds funny too.
I guess it should "spin" fast enough to keep the people from drifting away.
7919.59594928933 m/s should be the approximate velocity it should travel to give earth like gravity(assuming that it's inner radius is the same as that of the earth, and using a=(v^2)/r). Does Earth spin that fast?

[swansont]

But wouldn't Centripetal Acceleration give us gravity on the inside part of the ring? Assuming it is rotating along it's principal axis, ie perpendicular to the plane through the centre

Technically, no. But it would give an acceleration indistiguishable from gravity. You'd have "I can't believe it's not gravity!" ;)

[swansont]

Now that's a good thought. It sounds serious, but after a second look it sounds funny too.
I guess it should "spin" fast enough to keep the people from drifting away.
7919.59594928933 m/s should be the approximate velocity it should travel to give earth like gravity(assuming that it's inner radius is the same as that of the earth, and using a=(v^2)/r). Does Earth spin that fast?

If the earth spun so fast as to make the centripetal acceleration equal to g, we'd feel weightless (think astronauts in orbit) - so the answer has to be no. The earth spins at about v=40,000 km/86400 sec = 463 m/s at the equator.

[ski_power]

But that gives a CPA of hardly 0.03349515625 m/s^2, then how is it able to produce g(other than the Principle of Attracting bodies).
What if we lived in the inner part of the ring, then how much CPA would be needed to simulate near-earth gravity, assuming all identical earth properties.
And also, how come in the Astronaut Centrifuge, they are able to produce higher g that too with help of acceleration,

[swansont]

But that gives a CPA of hardly 0.03349515625 m/s^2, then how is it able to produce g(other than the Principle of Attracting bodies).
What if we lived in the inner part of the ring, then how much CPA would be needed to simulate near-earth gravity, assuming all identical earth properties.
And also, how come in the Astronaut Centrifuge, they are able to produce higher g that too with help of acceleration,

I'm not sure I understand the question - the value of ~8000 m/s would give ~1g for someone on the inside of the ring. That the earth rotates more slowly than this means we stick to the earth, rather than have a really low orbit around it. (ignoring the strong possibility that the earth wouldn't hold together at 8000 m/s)

We feel 1g on the earth because of the earth's mass and radius. The rotation actually decreases what we measure as our weight, by a fraction of a percent. But, as your numbers show, we can ignore the rotation for general discussions, since it's a small effect. To simulate earth's gravity, we'd need just under 8000 m/s, and be on the inside of the ring.

[ski_power]

Hey swansont, if the earth rotated at 8000m/s then it would act like a HUGE centrifuge. And then after a few million years, wouldn't earth become a torus?

[swansont]

Hey swansont, if the earth rotated at 8000m/s then it would act like a HUGE centrifuge. And then after a few million years, wouldn't earth become a torus?

No. Gravity at a radius R is dependent on the mass inside of R (for a uniform distribution). A torus has no mass inside, thus no gravity to hold it together. You might end up with a smaller planet that has rings, but that would depend on a lot of things.

[YT2095]

that effect is precluded by Gravity, however there is a very slight distortion, making the Earth not exactly a perfect sphere :)

[ski_power]

Hey wait, just for confirmation isn't torus a doughnut, with a hole in the centre?
This one
http://www.geom.uiuc.edu/zoo/toptype/torus/standard/gifs/front.gif
According to common sense, if the earth is flattened at the poles, due to spinning at the equator, shouldn't the same force assist further flattening of the planet?

[swansont]

Hey wait, just for confirmation isn't torus a doughnut, with a hole in the centre?

According to common sense, if the earth is flattened at the poles, due to spinning at the equator, shouldn't the same force assist further flattening of the planet?

Mmmmmm...donut :D

Flattening the earth is not the same thing as forming a torus. A disk still has mass in the center, but a torus does not.