Newton's second Law of Acceleration, Inertia and Momentum, Freefall

[Doc Al]

Buckley: The text you included in quote form does not appear in previous threads.

In appears in post #22 by TurtleMeister:

Edit:
I agree with you Buckleymanor. If Simon's thought experiment is carried out in the two phases that I mentioned, then A will hit the ground quicker than B (even when the math tells us that their accelerations are the same). Is this what you are having a problem with? Do you think that this contradicts the universality of free fall?

Folks, please use the "quote" feature properly, including the attribution of the quote so others can go back to the original.

 

[TurtleMeister]

Size seems to be the main problem with regards acceleration.

Physical size, or volume, is not relevant to the accelerations (assuming that there is no friction or drag).

The Earth does not rush towards a falling bowling ball at 9.8 mtrs/sec.

That is correct. The Earth does not accelerate at 9.8 mtrs/sec. But it does indeed accelerate toward the bowling ball, but at a much much slower rate. In fact, it would be so slow that we do not have instruments sensitive enough to detect it. What will help you here is to think in terms of momentum instead of acceleration alone. I will get to that in a moment.

However if the bowling ball was replaced with another Earth would it then rush towards it at that speed or twice as fast.

If the bowling ball were replaced with another Earth (earth2) then the acceleration of earth1 would increase, but the acceleration of earth2 would remain the same as the bowling ball. Whichever body you change the mass of, it will be the other body that changes acceleration. And it doesn't matter what the masses (sizes) are. If you increase the mass of a free falling bowling ball, it will be the Earth that changes acceleration, not the bowling ball. However, as stated before, this change in the Earth's acceleration would be very very small.

That brings us to the momentum that I mentioned. Imagine the two body problem where two bodies (M1 and M2) are accelerating toward each other under the influence of their own gravity. No other forces are involved. You know that momentum is mass times velocity, P=mv. Let's say that v1 is the instantaneous velocity of M1 and v2 is the instantaneous velocity of M2. Now it just so happens that the instantaneous momentum of M1 will always be the same as the instantaneous momentum of M2, |M1v1| = |M2v2|. Actually, this must be true at all times, otherwise the third law of motion and the conservation of momentum would be violated. So if we increase the mass of M1 then |v2| must increase. Likewise, if we increase the mass of M2 then |v1| must increase. And if M1>>M2 then |v1|<<|v2|.

 

[jeffrey c mc.]

So, third times the charm I guess, first time I dropped my keyboard and it caused a navigation, 'away', and dumped the text editor, second time I was about four sentences in and lost my internet connection, along with my browser; if it happens again I'll consider it to be someone else' 'will, and give up on it. Hey! Thanks Buckley, your direction to post 22 and additional material helped clarify the question. Simon, I have read the material on the links provided in thread #25. I have a better understanding in the textual comprehension needs of making scientific ideas clear and succinct, and hope that, that will improve my own writing in same. I found the discussion on 'bad astronomy' to be better, and more lucid in explaining the difference in the topic of orbital mechanics of--sic the Earth and moon--and the difference between two; comparatively smaller objects; caused to enter into a free-fall state; on one or the other. A point that Buckley expounded on, in his post, #30. I found that the material on 'bad astronomy' to be more lucid, as the material on 'bad physics' tended to became, somewhat jaded; as in semantically challenged; towards the end, with this:

[Note that just as the Moon exerts tidal forces on the Earth, the Earth exerts tidal forces on the Moon, deforming the Moon into a football shape with one tip pointing toward the Earth. The Moon was initially molten some 4.6 billion years ago, but retained this football shape when it solidified, and the Earth's tidal force keeps the long axis of the lunar football pointing toward the Earth. To keep the long axis always pointing towards the Earth, Moon spins once on its axis as it makes one revolution around the Earth. That's why we the same side of the Moon always faces the Earth.] http://www.jal.cc.il.us/~mikolajsawicki/ex_tides.html

Which; of course, I can not refute, and while it does offer a plausible explanation; even with that said, it seems to depart from the material on ' B.A.' just a tad. By the by, I was 9 in 1971; I remember the 'press video' from Vietnam; I remember Nixon, being a swell guy. Funny how memory works, upon watching 'Apocalypse Now', I got flashbacks from some of the scenes; even though they were re-creations, with soundtrack added, for value, I guess. I never knew what the heck Watergate was about until watching 'Forrest Gump' I knew it was some hotel, but I guess I also realized it wasn't about Nixon himself, and some gal, being caught, 'red handed' as one may say. I feel this is getting, or, going anywhere, so I'll dispense with it.

Thanks Doc Al, I'll review how the procedure for adding attributable quotes works, I've discovered how to add the quote tag around copy and pasted cites in advanced mode, now I'll have to review how, selecting text in-sitio, and adding it into a reply thread, is accomplished.

 

[jeffrey c mc.]

Turtlemeister;

I got finished with last post after your post #32. In another OP I was concerned about the usage of having two objects in, or described as occupying an one-dimensional construct. Is your description of describing the dynamics of just two objects and the characteristics of gravity dynamics, using such a principle? Also, is it not so that a violation of a natural law can happen, yet, if it does, it produces an anomaly, as phenomena. For example; the refraction of light, through a prism, or raindrop; the characteristics of an airfoil, or venturi, natural, or otherwise? It would seem that natural law, and the violation of same, happens, with, or without man's intervention. Sorry, may depart some from OP, and thread discussion, my first question may needs only apply.

 

[Buckleymanor]

Physical size, or volume, is not relevant to the accelerations (assuming that there is no friction or drag).

I don't see how this can allways be true.

That is correct. The Earth does not accelerate at 9.8 mtrs/sec. But it does indeed accelerate toward the bowling ball, but at a much much slower rate. In fact, it would be so slow that we do not have instruments sensitive enough to detect it. What will help you here is to think in terms of momentum instead of acceleration alone. I will get to that in a moment.

Yes.

If the bowling ball were replaced with another Earth (earth2) then the acceleration of earth1 would increase, but the acceleration of earth2 would remain the same as the bowling ball. Whichever body you change the mass of, it will be the other body that changes acceleration. And it doesn't matter what the masses (sizes) are. If you increase the mass of a free falling bowling ball, it will be the Earth that changes acceleration, not the bowling ball. However, as stated before, this change in the Earth's acceleration would be very very small.

When you say the acceleration of Earth 1 would increase I can't see how the acceleration would be very very small if you introduced an Earth 2.If you had two Earths you would have twice the mass they would both accelerate at 9.8 mtrs/sec and therefore the relative closing speed would double.
Gravity on the moon is a lot less than the Earth's and objects fall a lot slower because it's smaller.
Doubleing the size of the experiment by introducieng another Earth should have gravitational implications.
You say that it doesn't matter what the masses (sizes) are.If you increased the mass of Earth 2 beyond the size of the Earth then won't Earth 1 accelerate at a speed greater than Earth 2 towards it?
ie,more than9.8 mtrs/sec.

 

[TurtleMeister]

Turtlemeister;

I got finished with last post after your post #32. In another OP I was concerned about the usage of having two objects in, or described as occupying an one-dimensional construct. Is your description of describing the dynamics of just two objects and the characteristics of gravity dynamics, using such a principle?

I don't know what principle you're talking about. You may be able to answer the question yourself by googeling "two body problem".

Also, is it not so that a violation of a natural law can happen, yet, if it does, it produces an anomaly, as phenomena.

I think you meant "law of nature, or physical law" instead of "natural law". No, I've never heard of anything like that. The conservation of momentum, which I referred to in my post, is one of the most fundamental concepts of physics. There has never been an observation of it being violated. In other words, you can bet the farm on it.

Buckleymanor, you should try to fix your quotes before the edit time runs out. Make sure each quote has the "QUOTE=TurtleMeister;4375163" at the beginning and the "/QUOTE" at the end.

When you say the acceleration of Earth 1 would increase I can't see how the acceleration would be very very small if you introduced an Earth 2.

You are correct. Disregard the last sentence. I forgot that we were changing the mass of the bowling ball to the mass of earth. That's quite a change in mass. :)

You say that it doesn't matter what the masses (sizes) are.If you increased the mass of Earth 2 beyond the size of the Earth then won't Earth 1 accelerate at a speed greater than Earth 2 towards it?
ie,more than9.8 mtrs/sec.

Yes, that is correct. What I meant by saying "it doesn't matter what the masses are" is that it makes no difference as far as the UFF is concerned. You stated in a previous post; "When things are scaled up don't they get stranger". What I'm saying is, no they don't. It's still physics as usual.