Mascons

[swansont]

The sides aren't balanced that's kind of the point. Nature seeks balance.

Everyone keeps telling me that the two sides are balanced, but I can not see how they are, and that is why I cannot understand what they are saying.

 

You also haven't done any kind of rigorous analysis of it. You are assuming gravity behaves in a certain way, and it doesn't.

[elfmotat]

Are you saying that each arrow on the wheel has the same acceleration value?

 

No, I'm saying that the net force on the wheel provides no torque. I.e. you can't get any rotation out of it.

 

 

Without regard to what the acceleration value is over the moons surface?

 

Without regard to the wheels position?

 

Yes, I can tell you for sure that there will be no torque on the wheel.

[swansont]

You can break the problem down into the sum of two simple problems (one uniform mass and one to account for the inhomogeneity), neither of which produces a torque.

[jajrussel]

 

You also haven't done any kind of rigorous analysis of it. You are assuming gravity behaves in a certain way, and it doesn't.

You are right; I haven't, and I am making assumptions. Now I'll work on figuring out why you are right, and why my assumptions are wrong.

 

I know I can be hard headed, especially when something seems obvious to me. So thanks for everyone's patience.

[elfmotat]

A better answer for why you can't possibly get any torque on the wheel, regardless of the distribution of matter around it, is because gravity is a conservative force. This means there's no "circulation" in the field, so no matter how clever you are in positioning the wheel it simply will not rotate.

[swansont]

A better answer for why you can't possibly get any torque on the wheel, regardless of the distribution of matter around it, is because gravity is a conservative force. This means there's no "circulation" in the field, so no matter how clever you are in positioning the wheel it simply will not rotate.

 

Exactly. It's a vector and obeys superposition, and no matter how many masses you break it down into, none of the individual parts lead to a torque.

[imatfaal]

!

Moderator Note

 

itry

 

stop hijacking the thread with puffs for your own thread - this is not allowed. The first time you did this the post was hidden and I have now hidden the second.

 

Do not respond to this moderation within the thread

 

[jajrussel]

One of the thoughts I had that made me think it might work was that the article said the gravitational difference in the center of one of the mascons was equal to four ounces more than something that weighs fifty pounds at normal moons gravity. I am paraphrasing my understanding of what I read.

 

This seemed to mean, to me at least, that if I set up a scale and put fifty pounds on one side, and fifty pounds four ounces on the other, then stated pushing the scale with the fifty pound weight end toward the Mascon I should reach a point somewhat along the way where the scale would balance. This seemed to imply torque.

 

Then I thought if I did it again with fifty pounds on both sides of the scale. The side entering the Mascon first should begin to act as if it weighs () more then begin to drop. Again this seemed to imply torque.

 

Then I thought why not use a large perfectly balanced wheel.

 

I am assuming now that my thinking was wrong. Nothing that simple should actually work anyway. It would be way to simple.

 

I removed the words (four ounces) that were between the parentheses in editing because I realized that four ounces more would be a bit extreme.

 

Even if ones assumption is wrong, one should try to be more precise...

Edited November 10, 2014 by jajrussel

[imatfaal]

jajrussel - as a few of us have mentioned the way to see this most intuitively is to separate the the masses.

 

Draw two diagrams one with the moons mass (all of which can be seen as concentrated at the centre) and the other with just the mascons mass. Draw a line linking the centre of the moon and the centre of the wheel - are there any unbalanced forces? Its perfectly symmetrical and you can see that forces on one side balance the forces on the other. Do the same with a line drawn between the centre the mascon and centre of the wheel - the same thing applies. If all the forces from moon are balanced and all the forces from the mascon are balanced - why when you add them would you end up with imbalance?

[swansont]

One of the thoughts I had that made me think it might work was that the article said the gravitational difference in the center of one of the mascons was equal to four ounces more than something that weighs fifty pounds at normal moons gravity. I am paraphrasing my understanding of what I read.

 

This seemed to mean, to me at least, that if I set up a scale and put fifty pounds on one side, and fifty pounds four ounces on the other, then stated pushing the scale with the fifty pound weight end toward the Mascon I should reach a point somewhat along the way where the scale would balance. This seemed to imply torque.

 

Then I thought if I did it again with fifty pounds on both sides of the scale. The side entering the Mascon first should begin to act as if it weighs () more then begin to drop. Again this seemed to imply torque.

If you have an area of greater acceleration, the force won't suddenly "turn on"; you will have a force that is not directed toward the center of the moon.

 

You can have a torque in that situation, just as you could have one with a uniform gravitational field if the arm was not horizontal — the mass that's closer will experience a greater force. But the torque will cease when it's vertical. In the case with the mascon, there will be an equilibrium position as well. The torque is a transient condition.

 

Then I thought why not use a large perfectly balanced wheel.

Symmetry ensures you cancel out any non-equilibrium scenarios described above. Every mass element has a pairing such that there is no net torque.

[jajrussel]

I am still working out what the two off you have said, basically so I can quit using my head to do all the work.

 

While I was thinking of a diagram I realized that my thoughts on direction were too limited. Pretty much straight up and down with a slight angle toward the moons center.

 

Every part of the moon is attracted to every part of the wheel, and every part of the wheel is attracted to every part of the moon. In a sense everything flattens out, and the difference in acceleration from one side to the other was negligible to begin with.

Edited November 10, 2014 by jajrussel