Physics of Artificial Gravity....

[essenmein]

On the AG vein, had a thought/question re the work that it is doing, by work I mean joules.

So, AG generator is on the ship, as are the occupants. So relative to the AG generator (assume for the time being no one is moving on the ship) the things the generator is acting on are not moving relative to itself. Since I imagine to cancel the forces a body experiences due to an acceleration, the AG generator must provide a force in the opposite direction, basically canceling that accelerating force. Since it is applying a force but no motion is happening, no work is done. So power requirements are zero? Or would that work move to an external reference frame?

Then from a structural perspective, would all the forces the generator is canceling be put back on it? Ie my mass might appear zero, but the reaction from my mass is put onto the generator?

Or is this best left untouched because it is not real lol.

<edit: corrected incorrect wording on question>

 

[anorlunda]

Isn't an AG machine also a free energy machine?

AG on, lift the mass high in the air with zero work. AG off, let the mass generate power as it comes down.

You know that PMMs and free energy aren't allowed on PF.

 

[essenmein]

Isn't an AG machine also a free energy machine?

AG on, lift the mass high in the air with zero work. AG off, let the mass generate power as it comes down.

You know that PMMs and free energy aren't allowed on PF.

<edit: Just realized after writing response that I wrote the title wrong, it should be "artificial" not "anti"!>

I guess that was the question really, and I hope discussion is at least ok in the science fiction side of things, since its fictional. I think there is a difference between anti gravity, something that magically makes gravity go away, and a gravity generator, which is generating a local canceling field. This canceling already happens, there is a zero G spot at the right distance between the Earth and the moon where the pull on my mass from the moon is identical to the pull from Earth resulting in zero net force on me. From a spaceship perspective this is the goal, manage the net forces on the internals, I would assume that this does not mean that nothing experiences those forces.

I assume that its like a magnetic field, when a magnet lifts something, it appears to be moving with nothing touching it, but there is a reaction on something (the source of the field). So I have to assume if you could generate a gravity field, the forces that field is exerting manifest themselves as reaction forces in that generator. So I'm not sure simply being able to generate a gravity field automatically leads to a self levitating devices ala star wars, we can't do that with magnets either.

I think that I'm going to have the engines and the artificial gravity generators linked somehow, the engines push on the Field generators that essentially aggregate all the reaction forces from the ships' mass into them.

 

[stefan r]

An artificial gravity device would be just as much free energy as the anti-gravity. A generator at a reservoir/dam is basically attached to a pipe. Today we can pump water back up into the reservoir and use it as power storage but lose about 20% of the energy. With an artificial gravity you don't need the reservoir or the pump. Water or some fluid flows through loop. Put the artificial gravity device on the downward stretch. The extra weight will be enough to drive the turbine and also push the fluid through the cycle. Alternatively you could apply the artificial gravity to one side of a fly wheel. If you can switch AG on and off quickly you could drive a piston with a spring.

The AG device could be interesting if you scale it up. Why not 10^9 g? Would be useful for chemistry. Maybe fusion. Why not a big field? We could boost fusion rates in stars or ignite planets. An AG device might be useful for making micro black holes.

 

[Rive]

Strictly on energy conservation basis I would expect the AG generator consume adequate amount of energy to supply (remove) all the potential energy generated (eliminated) within the bubble of effect (in case there is no limited size bubble of effect then this is to be extended to the whole universe) >>some smug face smiley to be inserted here<<.

 

[stefan r]

Strictly on energy conservation basis I would expect the AG generator consume adequate amount of energy to supply (remove) all the potential energy generated (eliminated) within the bubble of effect (in case there is no limited size bubble of effect then this is to be extended to the whole universe) >>some smug face smiley to be inserted here<<.

We could throw some rotting banana peels and stale beer into the AG device. Similar to the mr fusion device in Back to the Future II. Powering it using dark matter might help stifle questions about "how this works".

 

[essenmein]

From a conservation of energy perspective I think I'll treat the artificial gravity generators like a 2 quadrant motor controller, to accelerate an object requires power, to decelerate that object, the artificial gravity generator is returning power.

 

[Rive]

...to decelerate that object, the artificial gravity generator is returning power.

That would be still too fishy I think. Maybe a bit less organized way? Let it return heat only.

 

[essenmein]

That would be still too fishy I think. Maybe a bit less organized way? Let it return heat only.

Heh like a friction brake! Thermal radiation plates glow brightly when the ships are slowing.

 

[russ_watters]

On the AG vein, had a thought/question re the work that it is doing, by work I mean joules.

So, AG generator is on the ship, as are the occupants. So relative to the AG generator (assume for the time being no one is moving on the ship) the things the generator is acting on are not moving relative to itself. Since I imagine to cancel the forces a body experiences due to an acceleration, the AG generator must provide a force in the opposite direction, basically canceling that accelerating force. Since it is applying a force but no motion is happening, no work is done. So power requirements are zero? Or would that work move to an external reference frame?

Then from a structural perspective, would all the forces the generator is canceling be put back on it? Ie my mass might appear zero, but the reaction from my mass is put onto the generator?

Or is this best left untouched because it is not real lol.

If you are looking to describe this for sci-fi purposes, I would consider it similar to electromagnetism: a static electromagnet can indeed produce a large force with a small energy input whereas a motor is an electromagnet in motion and consumes much more power.

 

[essenmein]

An artificial gravity device would be just as much free energy as the anti-gravity. A generator at a reservoir/dam is basically attached to a pipe. Today we can pump water back up into the reservoir and use it as power storage but lose about 20% of the energy. With an artificial gravity you don't need the reservoir or the pump. Water or some fluid flows through loop. Put the artificial gravity device on the downward stretch. The extra weight will be enough to drive the turbine and also push the fluid through the cycle. Alternatively you could apply the artificial gravity to one side of a fly wheel. If you can switch AG on and off quickly you could drive a piston with a spring.

The AG device could be interesting if you scale it up. Why not 10^9 g? Would be useful for chemistry. Maybe fusion. Why not a big field? We could boost fusion rates in stars or ignite planets. An AG device might be useful for making micro black holes.

I think this is only true if the artificial gravity field generator is not consuming power proportionally to the work its doing, and this is the thing that I was trying to get straight.

I keep coming back to the magnetic analogy, when we use a magnetic field to create a static force, no work is done and the only energy consumed are the losses in the system, but as soon as the object experiencing the forces starts to move, back emf is generated and the magnetic field generator is now consuming power to move that object with the field.

Are gravity fields analogous to magnetic fields? for example if gravity flux density was a thing, if you integrate this gravity field over a closed surface, is the result zero?

 

[snorkack]

Are gravity fields analogous to magnetic fields? for example if gravity flux density was a thing, if you integrate this gravity field over a closed surface, is the result zero?

In terms of Maxwell equations, gravitostatic fields are analogous to electrostatic fields. Both have been observed to have nonzero source terms (charge in case of electrostatic field, mass in case of gravitostatic field), whereas electromagnetic monopoles have not been seen again since Valentine´ s Day 1982, and gravitomagnetic monopoles have not yet been observed.
Note that in absence of sources, electric and magnetic fields are indistinguishable. Changing electric field as displacement current induces electromagnetic field, and changing electromagnetic field induces electric field. Electromagnetic waves are symmetric against interchange of electric and magnetic fields. Likewise, gravity waves are symmetric against interchange of gravitostatic and gravitomagnetic fields.

A difference between electrostatic and gravitostatic forces is that for gravitostatic forces, only one sign of source has been observed so far, compared to two signs of electric charges, and that the gravitostatic force between like sources is attractive, vs. repulsive in case of electric charges.

You can easily exclude electric field from a volume of space, by a Faraday cage. Faraday cage is not free energy. For a Faraday cage also disturbs electric field outside the cage.

With a difficulty, you could also build a Faraday cage to exclude gravity field from a volume of space. The difficulty is that while charges in a conductor would spontaneously flow wherever needed to counteract the external electrostatic field, you would have to actively do work to lift weights to your ceiling until their gravity counterbalances Earth gravity, and then actively fit the weight distribution to achieve precisely zero gravity throughout the cage.

 

[Vanadium 50]

I have a bit of a cold, so am a bit grumpy, and sneezy, and if take some medication it might make me dopey, but still..

I didn't want this section established, in part because of threads like this. We can't really talk about what established science says about anti-gravity because established science says there isn't any such thing. We can talk about how fictional science might behave - for example, anti-gravity is a shielding effect of, I dunno, let's call it "Cavorite" which can move but not destroy gravitational field lines, much as mu-metal does with magnetic field lines. (This will fix your conservation of energy problem) But in that case, the final product is not the product of the author's imagination, but rather PF's. Or whomever PF cites.

Cavorite...cavorite...I've heard that somewhere before...

 

[Bystander]

Cavorite...cavorite...I've heard that somewhere before...

+1

 

[snorkack]

I didn't want this section established, in part because of threads like this. We can't really talk about what established science says about anti-gravity because established science says there isn't any such thing. We can talk about how fictional science might behave - for example, anti-gravity is a shielding effect of, I dunno, let's call it "Cavorite" which can move but not destroy gravitational field lines, much as mu-metal does with magnetic field lines. (This will fix your conservation of energy problem) But in that case, the final product is not the product of the author's imagination, but rather PF's. Or whomever PF cites.

Cavorite...cavorite...I've heard that somewhere before...

First Men on the Moon.
And the classic, Wells´ cavorite did expressly destroy gravitational field lines. Which, once you think about it, specifically does not conserve energy - though Wells flinches from outright stating that. Demonstrated by two applications, though. The intentional one - lifting the spaceship out of Earth gravity well. Of course, cutting off field lines eliminates potential energy of the ship. And the unintentional one, which blows up a house.
This is actually not how Earth gravity works: because Earth mass is actually not all in the centre. But having a cavorite sheet which cuts off gravitational field lines is liable to cause unintentional operation of perpetuum mobiles by causing a gravitomotive field. Which is a problem you should be alert to when producing any cavorite whatsoever.

 

[member 656954]

I didn't want this section established, in part because of threads like this.

Sorry to hear you're unwell, @Vanadium 50, but I at least appreciate that PF has this forum as it does assist put the 'science' in sci-fi wherever that's possible.

Though, I do agree, AG is not science and any question about it can only really be answered with "what does the plot need it to do?" I note that luminary authors such as Peter Hamilton, Iain M. Banks, and Richard Morgan all routinely use AG but none of them have tried to describe it, and as a reader, I just go along with it because a detailed treaty on gravimetric field forces...or cavorite...is unnecessary.

It's good that @essenmein wants to at least think it through and build a consistent worldview of AG, but very few readers will extrapolate these threads in the plot into perpetual motion machines etc., but at some point as an author you have to adopt a QM analogy for science fiction: "Shut up and write!"

 

[Vanadium 50]

a detailed treaty on gravimetric field forces...or cavorite...is unnecessary.

To suggest is to create. To define is to kill. (Mallarmé)

 

[Lren Zvsm]

Sorry to hear you're unwell, @Vanadium 50, but I at least appreciate that PF has this forum as it does assist put the 'science' in sci-fi wherever that's possible.

Though, I do agree, AG is not science and any question about it can only really be answered with "what does the plot need it to do?" I note that luminary authors such as Peter Hamilton, Iain M. Banks, and Richard Morgan all routinely use AG but none of them have tried to describe it, and as a reader, I just go along with it because a detailed treaty on gravimetric field forces...or cavorite...is unnecessary.

It's good that @essenmein wants to at least think it through and build a consistent worldview of AG, but very few readers will extrapolate these threads in the plot into perpetual motion machines etc., but at some point as an author you have to adopt a QM analogy for science fiction: "Shut up and write!"

Good points, but we should also remember that we don't need to include our worldbuilding in the stories that we write: all we have to do is make sure that the action conforms to our worldbuilding. For example, if our speculation about artificial gravity suggests that it has side effects, we need mention the side effects only if they are relevant to the story and we need not mention the reasons for the side effects at all.