OT: Ceres more interesting than previously thought

[inigma]

Oh and the coin idea would be great, if it weren't such an engineering challenge to create a transparent material strong enough to hold back an ocean of water from flinging into space.

And I don't know if such a boat would float like earth ships, because unlike earth, the deeper in the coin ocean you go, the stronger the centripetal force. I wonder if such a force would practically suck ships down.

Imagine the fish in such an ocean... stuck to the bottom because it takes effort to "climb" up. Swimmers would sink faster than they can float... and boats would have their fishing lines be the straw the breaks the camel's back and starts a chain reation that sucks the whole ship down to the bottom with increasing velocity. Not to mention the force of such a slam on the transparent plating holding in the water.

Sounds like fun!

[Wolfman77]

Give the size, the gravity change (or force acting like gravity) would not be that sudden. also the water would not need to be that deep, there should only be a few percent difference from the surface to the floor. Even if there was a large change, remember that the water is pulled down just as hard as anything in it. The force that keeps us floating (or swimming)is the pressure of the water below is larger than that above. This would still apply, and a more sudden change in force would magnify this, making it harder to get to the outside wall.

[inigma]

I would think that it works in theory. But practically, it'd be quite the challenge.

I think it would far easier to build self-replicating robots which would automatically plant rockets on nearby asteroids and slowly drive them towards Ceres for a concerted accretion.

[NullAshton]

I think we could just wait till we have artificial gravity.

[Hunpecked]

If an object's average density is less than water, then it will float in water under one gravity, two, or fifty. However, boat and submarine hulls would be under increased pressure under higher G.

[narf poit chez BOOM]

It would take more energy for it to spin slower, and more mass for it to spin faster.

...Did I miss some basic physics here? Last time I checked, heavier things need more energy to move, and more energy makes things go faster.

[inigma]

narf poit chez BOOM said:

...Did I miss some basic physics here? Last time I checked, heavier things need more energy to move, and more energy makes things go faster.

Mass and energy convert between one or the other. The thing with gravity is, you need mass not energy.

Since I believe the spin of a body in space is naturally dependent on mass, by adding mass the spin would increase. By adding energy (which cancels out mass) spin would decrease.

[Suicide Junkie]

inigma said:

Mass and energy convert between one or the other. The thing with gravity is, you need mass not energy.

Since I believe the spin of a body in space is naturally dependent on mass, by adding mass the spin would increase. By adding energy (which cancels out mass) spin would decrease.

Heck no.
E = MC^2, remember? Increasing energy -> increasing mass (by a very small amount since c^2 is huge)

The angular momentum of a body depends on its shape, mass and spin rate.
If you make the object smaller it spins faster since the angular momentum must be conserved.
If you add mass without changing the angular momentum, the body will be spinning slower because there is only so much momentum to go around.

The spin of an asteroid is essentially random as the tiny rocks whang it from random directions at random speeds. However there is an upper limit to how fast they could be spinning, since they are generally not solid bodies.
If they spin too fast then rocks on the surface will be swung off by the centrifugal force, and the asteroid breaks up.

[inigma]

If they spin too fast then rocks on the surface will be swung off by the centrifugal force, and the asteroid breaks up.

That's my point. To generage 1G of centripetal, the astroid would fly apart, or be so big that you wouldn't need to hollow out the core.

E=MC^2 does not take into account gravitational physics. Einstien couldn't figure out exactly how it played into it.

It is my belief that mass contributes to the natural spin of a body in space-time, up to a certain equilibrium point.

Even though you are correct that initially adding mass to Ceres would cause it to slow down, equilibrium would be reached over time and it would naturally speed up by gravitational physics up to a certain point of equilibrium.

Adding too much mass would obviously cause Ceres to spin down too quickly and the weakened gravity well would essentially force Ceres apart.

What I'm essentially saying is that the faster mass moves, the greater the gravity effect - up to a certain point of course where centripetal force starts to overcome object's structural integrity. This is all due to the increase in mass as energy is converted to mass to move something faster.

By forcing Ceres to spin faster, that balance is offset, and eventually cetripetal force will fly it apart. Mathematically, for purposes of this coin idea, I can guestimate that the centripetal force of a spinning body can never be greater than its optimal gravitational force (and structural integrity).

In short, by the time you could spin Ceres to 1G centripetal force, its would fly apart as 1G of centripetal force would be greater than the escape velocity of the surface which is dependent on the equilibrium of 0.03Gs (guessing its 0.03Gs) generated by Ceres.

That 0.03G is what is holding Ceres together. Force Ceres to spin at a 1G centripetal rate, and you can imagine the concequence.

[Suicide Junkie]

What the heck are you talking about? Where did 1G come in?

And WTF is "natural spin"? There is absolutely no preferred spin direction around here in the universe.

Adding too much mass would obviously cause Ceres to spin down too quickly and the weakened gravity well would essentially force Ceres apart.
No way.
More mass -> more gravity.
Slower spin -> less centrifugal force.
Which means objects on the surface feel even more force downwards.
The rate of mass change is completely irrelevant.

This is grade nine or lower physics here.
Please, look up ANGULAR MOMENTUM.