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

[jeffrey c mc.]

Okay, we have one-thousand pounds; at sea level, and a feather. We elevate them to a thousand meters and support them on a platform. All of which is in a vacuum. We remove the platform, they both hit the earth; the limiting surface; at the same time. Newton's second law suggests that this is due to the inertia of the the heavier object. Due to its' inertia it is slower out of the gate. Also a discussion of force and mass needs to be elucidated. Yet, momentum, is a hyperbolic function that is calculated by mass, distance moved, and rate of change, actually it's mass times velocity; but since the acceleration of gravity is inversely tied into the square of the distance traveled (or the distance between the two gravitating bodies) [sic ie. free-fall], one would think that in free-fall, a discussion of how far the object has traveled would be interesting to know, in the grand scheme of it, I dare say.

Any thoughts would be appreciated. The 'one' in the fifth sentence, that is; is myself of course, no implication that others may, or might think this, need apply.

Jeffrey

 

[Simon Bridge]

I'm thinking that there is no question in there.
The observation about momentum is not inconsistent with the previous observations about force so it does not deserve the "yet"... yet - so what?

I wonder why you left off the mass-dependence of Newtonian gravity - perhaps this is the mass-force discussion that should be elucidated from you?

 

[jeffrey c mc.]

Simon, thank you for the response. Yes, I haven't posed the question sufficiently, or correctly. Your statements are valid. I also see that I need to be even more succinct in my language from your discussion on my use of 'yet.' I observe that the language of science is even more exact then what I am apt to but it to, as I say. My observations are built around the idea that gravity is an accelerative force and tied in with mass. Both the mass of the gravitating object, and the falling object. So, while both objects are in free-all. Both objects are gaining a net increase in force--which is slaved to their mass--the closer they get to the gravitating object, they are approaching. So, from the independent viewpoint, they are not receiving a net-force increase, but, from an internal aspect, the larger mass is receiving a net force increase, the closer it gets to the gravitating body. Therein lies the crux of the conundrum--my conundrum--why is it they hit the limiting surface at the same time, in a vacuum.

http://www.physicsclassroom.com/Class/newtlaws/U2L3e.cfm

So the lesson seems to suggest that only the gravitation of the gravitating body--the Earth sic-- applies; which suggests to me, that it--aka the gravitating body--is a rather singular thing, then I wonder why my original statement of the problem was rejected through moderation, by Dale-spam?

Once again thank you for the opportunity to sharpen my language skills--or lack of same, heh--and to realize that knowledge is a discourse between competing minds, and does not happen in a vacuum, or so they say. Although some might retort that my mind is a vacuum, which could have two different meanings, similar to Schrodinger's Cat musings, only better. Heh!

 

[DrewD]

Simon, thank you for the response. Yes, I haven't posed the question sufficiently, or correctly. Your statements are valid. I also see that I need to be even more succinct in my language from your discussion on my use of 'yet.' I observe that the language of science is even more exact then what I am apt to but it to, as I say. My observations are built around the idea that gravity is an accelerative force and tied in with mass. Both the mass of the gravitating object, and the falling object. So, while both objects are in free-all. Both objects are gaining a net increase in force--which is slaved to their mass--the closer they get to the gravitating object, they are approaching. So, from the independent viewpoint, they are not receiving a net-force increase, but, from an internal aspect, the larger mass is receiving a net force increase, the closer it gets to the gravitating body. Therein lies the crux of the conundrum--my conundrum--why is it they hit the limiting surface at the same time, in a vacuum.

http://www.physicsclassroom.com/Class/newtlaws/U2L3e.cfm

So the lesson seems to suggest that only the gravitation of the gravitating body--the Earth sic-- applies; which suggests to me, that it--aka the gravitating body--is a rather singular thing, then I wonder why my original statement of the problem was rejected through moderation, by Dale-spam?

Once again thank you for the opportunity to sharpen my language skills--or lack of same, heh--and to realize that knowledge is a discourse between competing minds, and does not happen in a vacuum, or so they say. Although some might retort that my mind is a vacuum, which could have two different meanings, similar to Schrodinger's Cat musings, only better. Heh!

The force on the falling body is $F_g=mg$ where $m$ is the mass of the object and $g$ is a coefficient that depends on the mass of the Earth (and the distribution of mass). The force then depends on the Earth and the mass of the body. The reason that both objects fall toward Earth in the same amount of time is because mass not only (partially) defines the force of gravity but also defines the resistance to acceleration (inertia). If only the Earth mattered, then lighter objects would hit first since the force on both the heavy and the light object would be the same, but the heavier object would have more inertia.

I bet that the reason that a Mod rejected your other post is because it was totally incoherent and you misused almost every word that you used. Singular and singularity have a few very specific meanings in mathematics and in no way add to your question/rambling. If you want to ask questions and you don't understand the subject, you should stick to simple words, few words, and, well, ask a question.

From your OP, it seems to me that you have very little understanding of force and momentum. If you are using other sources to study, it would be best to ask straight forward simple questions about the specific thing that you read rather than saying weird things like "momentum, is a hyperbolic function".

 

[Bandersnatch]

Due to its' inertia it is slower out of the gate.

This is the false assumption in your reasoning that produces the expectation of different times of impact.
The reason why it is wrong has been explained above in DrewD's, perhaps a tad too grumpy, post.

If it's still unclear, consider the thought experiment wherein you divide the thousand pound mass into a multitude of tiny masses, each equal to, say that of a feather.
According to your reasoning, this 1000-pound mass should now fall slower, because nothing's stopping you from treating each individual feather-bit of the original mass as a separate falling body with lower inertia.
This produces a paradox where the same body can fall at different speeds depending only on your mathematical considerations, so it's an indication of a faulty reasoning.


To restate DrewD's explanation again, all masses equidistant from the central body accelerate at the same rate in its gravitational field, thanks to the force of gravity scaling with mass of the body being attracted.

 

[DrewD]

...DrewD's, perhaps a tad too grumpy, post...

Fair enough; I hadn't finished my coffee. Sorry to be rude, Jeffrey, but I do think that simple language works well.

 

[jeffrey c mc.]

Thank you all for your discussion. I am not a physics student, yet I have received basic training in Aviation maintenance which covered theories of thermodynamics, gases, and heat; fluid dynamics, hydraulics, and flow movement, combined with gases, viz carburetors; gas dynamics, once again, carburetors, viz venturi effects, aerodynamics, airfoils; basic electricity; weights and balance, force; and how to sew a fabric covering together on old aircraft; added that just for whimsey, heh!. I incurred this in an Aviation maintenance course in the military, and a two year applied, Airframe and Power-plant course; unfortunately this was thirty years ago, and I may be a little out of touch with my demonstrable knowledge of same. And yes, your remarks are well stated, my use of terms is not coherent with those that have had a classical training in scientific knowledge; I will try to get up to speed with the terms I attempt to use to either ask questions or state my understanding of scientific principals; and I will either not use a term if I am un-clear about how it is used in the appropriate context, or follow the advice of Drew and ask, or relate my thoughts in a more general fashion.

With that said, I will also use the primer of the link to try to see if I can follow the discussion and suggestions Drew gave in his response. I'll be back if I can think of some clever way to confuse myself more. Heh.

Jeffrey

P.S. There was a discussion on the site I provided the link for about the idea Drew was discussing but I need to explore it further before I can relate much about it. Something about the ratio of the acceleration of gravity, which is the principle behind Drew's discussion.

P.S.S I only used hyperbolic because someone else used it on me, they got all hyper-colic on my a**.

Actually I was describing something as having an increased peak force as the evolution progressed; a graph sloping upward at an increasing rate at constant intervals; so to say. Or, a marked increase at each regular interval; one half of a bell curve; the acceleration of gravity. As gravity is inversely proportional to the square of the distance separating the two objects. What, 9.8 meters per second, per second. Something along those lines, I do assert.

More to follow

Jeffrey

 

[jeffrey c mc.]

If Newton's second law were applied to their falling motion, and if a free-body diagram were constructed, then it would be seen that the 1000-kg baby elephant would experiences a greater force of gravity. This greater force of gravity would have a direct affect upon the elephant's acceleration; thus, based on force alone, it might be thought that the 1000-kg baby elephant would accelerate faster. But acceleration depends upon two factors: force and mass. The 1000-kg baby elephant obviously has more mass (or inertia). This increased mass has an inverse affect upon the elephant's acceleration. And thus, the direct affect of greater force on the 1000-kg elephant is offset by the inverse affect of the greater mass of the 1000-kg elephant; and so each object accelerates at the same rate - approximately 10 m/s/s. The ratio of force to mass (Fnet/m) is the same for the elephant and the mouse under situations involving free fall. [http://www.physicsclassroom.com/Class/newtlaws/U2L3e.cfm]

This is what I was reviewing when I came out with the, 'It's slower out of the gate' metaphor. Slower out of the gate means it takes--due to its' inertia-- longer to get moving. It would seem I have been following your objections before you made them. Using colorful colloquial speech rather then using terms I 'do not understand.' Here's another conundrum derived from your remarks. If the force is distributed throughout both falling bodies, then, the smaller body has the greatest concentration of force as it is smaller. They both are equal in that they hit the same limiting surface at the same time--in a vacuum; therefore, the gravitating force is diffused over a larger mass in the large body.

This ratio (Fnet/m) is sometimes called the gravitational field strength and is expressed as 9.8 N/kg (for a location upon Earth's surface). The gravitational field strength is a property of the location within Earth's gravitational field and not a property of the baby elephant nor the mouse. All objects placed upon Earth's surface will experience this amount of force (9.8 N) upon every 1 kilogram of mass within the object. Being a property of the location within Earth's gravitational field and not a property of the free falling object itself, all objects on Earth's surface will experience this amount of force per mass. As such, all objects free fall at the same rate regardless of their mass. Because the 9.8 N/kg gravitational field at Earth's surface causes a 9.8 m/s/s acceleration of any object placed there, we often call this ratio the acceleration of gravity. (Gravitational forces will be discussed in greater detail in a later unit of The Physics Classroom tutorial.) [same as first cite]

So, that's all well and good, except we are not talking about objects resting on the Earths surface---{Because the 9.8 N/kg gravitational field at Earth's surface causes a 9.8 m/s/s acceleration of any object placed there, we often call this ratio the acceleration of gravity.}[from cite]---we're talking about objects falling, which by definition are not resting on the surface of the Earth. So objects are accelerating when placed on the surface of the earth, they assert.

So, I hope I've demonstrated that I can read at least.

In all my replies I have made in this forum I have been consistent in humbling myself, and deferring to others; due to the fact that I do realize my classical training in the subject is abject and wanting; and I do realize that my basic knowledge of the proper terms and the usage of same; is also wanting. Yet I do not need to be reminded of it constantly; especially after I have acknowledged that in a previous reply, in the same thread.

And again; [So the lesson seems to suggest that only the gravitation of the gravitating body--the Earth sic-- applies; which suggests to me, that it--aka the gravitating body--is a rather singular thing, then I wonder why my original statement of the problem was rejected through moderation, by Dale-spam? ] (from third thread #3) This use of 'singular' is out of context in this thread, and OP. It makes a reference to an earlier started thread by myself, which quickly went into moderation and was removed as it was deemed not appropriate. Therefore, when I reviewed the discussion at the link I provided in my reply to Simon, I found it to say just about what I expressed in the post that was removed, so I began this thread. Only using ideas and concepts garnered from the aforementioned site link. I do hope no one wishes to claim that site is not a valid reference site. If we are to descend to that level of discourse that would leave me free to cast dispersions on this site also, I suppose.

Once again I do realize my reasoning skills may not be sufficient, and if you wish to point them out with demonstrations include, I won't cry foul, yet I may state my thoughts about the content, as I did with the above cite(s) pulled from another site{hopefully a site that all can consider to be a valid ref site); if I feel the only point being made is that I lack the superior reasoning, that others are endowed with, by the virtue of having a classical training in the fields of interest.

 

[Simon Bridge]

'It's slower out of the gate' metaphor. Slower out of the gate means it takes--due to its' inertia-- longer to get moving.

And that is a misleading analogy - which should become apparent when you try to quantify the speed out of the gate. How much slower is the bigger mass out of the gate?

In fact, both masses have the same acceleration - neither is any more prompt from the gate that the other.
I can kind-of see what you mean but on balance - give up the metaphor: you'll get further.

You keep making a distinction between the two bodies in question, calling one the "gravitating body" and the other something else. You should realize that both bodies are gravitating.

In many examples, an approximation may be made where one body is much much more massive than the other, and greater in extent, so that, from the point of view of an observer on or close to the surface of the big body, small bodies fall towards "the ground" with a constant acceleration.

Note "colorful colloqual speech" is not useful for finding out about technical subjects - as your training and practice in aviation maintenance should have lead you to discover. Fuel burns, the ground is hard, and so on - pilots and engineers who mess about with those description on the job get into trouble. How would you feel towards a pilot who lapsed into poetic language in a report?

I'm still not sure that you have articulated your problem though.
Mostly you seem to be puzzled by some stuff you have read.

I suspect you will be best served by phrasing your puzzlement as a series of questions.
What is it that you don't understand about gravity?

 

[jeffrey c mc.]

[And that is a misleading analogy - which should become apparent when you try to quantify the speed out of the gate. How much slower is the bigger mass out of the gate.]

Inertia is an inverse function(affect) of mass in acceleration. Acceleration is dependent on Force, and Mass; so says Newton.

{And thus, the direct affect of greater force on the 1000-kg elephant is offset by the inverse affect of the greater mass of the 1000-kg elephant; and so each object accelerates at the same rate - approximately 10 m/s/s. The ratio of force to mass (Fnet/m) is the same for the elephant and the mouse under situations involving free fall.} Not my content, it's from independent reference source, sic

[You keep making a distinction between the two bodies in question, calling one the "gravitating body" and the other something else. You should realize that both bodies are gravitating.]

Yes that's a correct statement, because gravitating is a word that means being under the influence of gravity. My postulate is that the Earth, which is by all means a gravitating body, has a singular nature, then objects that are subject to the Earths gravity field. All things (objects) are subject to gravity, to be sure; though with the demonstration of two falling objects--in a vacuum--one could suppose that they--the falling objects--do not share the same nature, as the Earth, and the Earth's Gravity field.

[n many examples, an approximation may be made where one body is much much more massive than the other, and greater in extent, so that, from the point of view of an observer on or close to the surface of the big body, small bodies fall towards "the ground" with a constant acceleration.]

Every object in a Gravity field falls at a constant rate of acceleration. 9.8 meters per second, per second, to be succinct

[I'm still not sure that you have articulated your problem though.
Mostly you seem to be puzzled by some stuff you have read.]



The force of gravity is inversely proportionate to the product of; Mass, and the square of the distance between two objects in question. Acceleration is proportionate to the product of the; Mass, and Force applied. Unless I've learned my lesson incorrectly.

Therefore, even while the Acceleration of Gravity is a constant; the altitude of an object, and it's mass, has a direct bearing on; the initial force as it rests on a platform; the net force 'increase' as it gets closer to the object it is falling towards; and, as Acceleration is tied into force and Mass; an object that has a larger Mass should receive a higher 'net force' increase--the closer it gets to the center of an object it is falling towards--then an object with a dramatic decrease in it's mass; as set against the larger object. Yet, in free-fall, in a vacuum, they arrive at the limiting surface--the same limiting surface--together. And yes, this puzzles me! And yes, I'm still working with the ideas and concepts I received from the source material.

Contrary to the impression I am likely to be seen as projecting, I am here to learn, and do welcome discourse and debate; but, just as I have to learn the proper use of terms that are applicable to the fields in question; I would ask that others be a little patient with me; and make the attempt to work around my 'world-view' and the way I express it.

citations
[brackets] are cites from Simon's discussion. {fancy brackets} are full citations--meaning no exclusion of content from bracket to bracket--from independent source. Paragraphs that start with no diacritical marks comprise my thoughts.

 

[Bandersnatch]

You're still missing the point we(and the source you're citing) are trying to convey.

Yes, more massive objects have higher inertia - they require higher force to accelerate in the exact same way as less massive objects. If you supply twice as high a force to twice as massive a body, it'll have the exactly same acceleration, at all times.
The force of gravity scales with mass, so it will always provide exactly enough extra force to move any object(equidistant from the source) at the same rate.

Take a look at the equations:

Newton's 2nd Law of Motion is expressed by:

$F=ma$
$a=\frac{F}{m}$

Where F in Newtons is the force needed to accelerate the mass m in kilograms with a metres per second squared.

Integrating acceleration over time nets you all the remaining kinematic equations(velocity and position), so all you need for two bodies to move in an identical fashion is for the acceleration to be identical. With identical acceleration they'll have identical instantenous velocites and positions.

If you have two masses m and 2m, and you need both to move in exactly the same way(equal a), then you need forces F and 2F respectively.

Now, the force of gravity is given by:

$F_g=G\frac{Mm}{R^2}$

Where F_g is the force between the two bodies of masses M and m(M>m, by convention), separated by R metres. G is a constant.

Substitute F_g to the equation of motion to find out that:

$F=F_g$
$ma=G\frac{Mm}{R^2}$

and the result is:

$a=G\frac{M}{R^2}$

Which tells you that how the body moves in the gravitational field of mass M is independent of the object's mass. Whether you have a body of mass m(a feather) and gazzilion*m(an obese hippo), matters not, since their mass is absent from the equation of motion as shown above. As long as the two bodies begin their movement at the same distance R, and gravity is the only force acting, then they will always move in the same way.

 

[jeffrey c mc.]

Thank you Bandersnatch. I believe I understand my thinking error now. One; I was placing to much emphasis on Newtons second law of acceleration; which, is a general statement, as compared to the force of gravity, and acceleration of same. Which could be considered a specific, or special, phenomena. Where as I could be the one applying the force in the general nature to an object. Gravity is the supplier of the force in the specific, concerning objects in free-fall. I do understand that gravity, as a force is thought of as a constant, and is accelerative; ad is defined by Mass, and the inverse of the square of the distance between the center of two objects. Which provides the accelerative nature of gravity. So, when we have two objects on a platform, at an elevation, the masses of both can only be considered as potential. When the support is removed, both begin descent at appx the same time; the mass becomes kinetic. Yet the energy can only be realized if and when an obstruction is met. So, while they are in free-fall, the force of gravity acts on both equally. And even though the moment of inertia in the larger mass is greater, that energy only becomes manifest when it impedes on, or strikes a limiting surface, or something that can, and may cause a change in the force vector. Such as atmospheric drag.

So, I'm happy to retort my perplexity has lessened on this thread, and thank everyone who had the patience to continue remarking on my musings.

Jeffrey

 

[Buckleymanor]

And that is a misleading analogy - which should become apparent when you try to quantify the speed out of the gate. How much slower is the bigger mass out of the gate?

In fact, both masses have the same acceleration - neither is any more prompt from the gate that the other.
I can kind-of see what you mean but on balance - give up the metaphor: you'll get further.

You keep making a distinction between the two bodies in question, calling one the "gravitating body" and the other something else. You should realize that both bodies are gravitating.

Actualy is there not three bodies gravitating.The more massive one by far does not seem to move never mind it having the same acceleration as the others.Is the acceleration of small objects
mearly dependent on size with relation to the largest object.If one of them was scaled up to be more massive like say the size of the moon would it still have the same acceleration.
Things like kilo weights, elephant's and feathers are all insignificant in size in comparison to the Earth, so you would expect them to move with the same speed towards it and are common with our everyday experiance.When things are scaled up don't they get stranger.

 

[Jupiter6]

So, I'm happy to retort my perplexity has lessened on this thread, and thank everyone who had the patience to continue remarking on my musings.

Jeffrey

We've all been through the same line of thought at some point, whether we admit it or not.

One thing I'll point out is stop referring to gravity as a; "force", "g-force", "force of gravity" etc. It is not a force. When you stop referring to it as such, you'll make the mental connection more concrete and recognize what the f, m, and a in a real-life system are more easily.

Another biggie is understanding momentum and how energy relates to it (integral). Some "scientific" people seem to have a really hard time grasping the concept.

 

[Simon Bridge]

Actualy is there not three bodies gravitating.The more massive one by far does not seem to move never mind it having the same acceleration as the others. Is the acceleration of small objects merely dependent on size with relation to the largest object. If one of them was scaled up to be more massive like say the size of the moon would it still have the same acceleration.
Things like kilo weights, elephant's and feathers are all insignificant in size in comparison to the Earth, so you would expect them to move with the same speed towards it and are common with our everyday experience. When things are scaled up don't they get stranger.

Your language has become less poetic so it's easier to parse - well done.
Lets see if I can spot the questions in all that ...

Is the acceleration of small objects merely dependent on size with relation to the largest object. If one of them was scaled up to be more massive like say the size of the moon would it still have the same acceleration?

(Don't forget the question mark at the end of questions - they clue-in English speakers as to your intent.)
The acceleration due to gravity depends only on the relative positions of the gravitating objects and the mass of the other one. It does not matter what the size or the mass actually is.

If our two masses are $m$ and $M$ for the smaller and the larger mass, you have already realized that Newton's laws tell you (for the small mass):

$$\begin{array}{rrclr} & F & = & ma &\text{(1)}\\ \Rightarrow & \frac{GMm}{r^2} & = & ma &\text{(2)}\\ \Rightarrow & \frac{GM}{r^2} & = & a & \text{(3)}\end{array}$$​

... it does not matter how big $m$ actually is, the fact it appears on both sides of the equation means it cancels itself out.
If we were to scale m up to 1000000x the initial amount, then it would scale the same 1000000x on both sides of the equation in step (2) and still cancel out to have no effect on the acceleration (3).

What you or I may intuitively expect to be the case is not important. What is important is what is actually the case.

When things are scaled up don't they get stranger?

How do you mean?
Generally you cannot just scale up a bunch of dimensions and expect things to stay the same - no.
But there is nothing weird about that.

There are situations where Newtonian gravitation (what you have been struggling to understand above) does not apply - this is because it is, itself, a kind of approximation due to the investigative tools available to Newton and people of his ilk. A more complete picture of gravitation is provided by General Relativity ... this is why Jupiter6 is suggesting you stop talking of gravity as a "force": it can help with the transition to GR when you are finally ready for it. I think it's six of one and half-a-dozen of the other myself; but I'm pretty sure that your use of language is a major obstacle to your understanding here.

 

[TurtleMeister]

When things are scaled up don't they get stranger.

How do you mean?

He may be referring to the fact that if the mass of either body is increased, the time interval decreases (be it the period or the time to impact). This is often a source of confusion for folks learning Newtonian gravity because it seems to contradict the universality of free fall. The key to understanding why this is not a contradiction to the UFF is in understanding the frame of reference.

 

[Simon Bridge]

Sure... or it could be a reference to black holes, or something else.
But let's let OP tell us what OP means.

 

[Buckleymanor]

What you or I may intuitively expect to be the case is not important. What is important is what is actually the case.

I agree, so if we were to make mass 1 the size of the Moon, mass 2 a feather and mass 3 the Earth.
Then release mass 1 and 2 together slightly apart a thousand metres above the Earth.
Mass 1 and 2 won't hit the ground of the Earth together?
Even if the feather was released at the lowest possible levell point of the Moons circumference.

 

[Simon Bridge]

so if we were to make mass 1 the size of the Moon, mass 2 a feather and mass 3 the Earth.
Then release mass 1 and 2 together slightly apart a thousand metres above the Earth.
Mass 1 and 2 won't hit the ground of the Earth together?

3-body problem has no analytic solution.

Lets rewrite the thought experiment so the math is tractable.

Let there be two masses A and B with masses M and m respectively so that M>>m.
Let them fall under the uniform gravity approximation for objects close to the Earth - so the force of Newtonian gravity is Mg for mass A and mg for mass B.
Let mass A and B have equal, small, spherical volumes so that we don't have to worry about disparate sizes.
Now do the math - neglecting air resistance etc.

Now you can answer your own question.

 

[Buckleymanor]

Let mass A and B have equal, small, spherical volumes so that we don't have to worry about disparate sizes.

If A and B are equal in volume and mass they will hit the ground at the same time if they are not they won't.

 

[jeffrey c mc.]

Yes, from my understanding it is Mass that accounts for gravity. At least at the atomic level and higher. The Moon has a tidal force that is affecting Earth. If the Moon had a M of 5g, how would that effect the bodies of water on the earth? Even if it was near enough to provide, the proper calibration to make the appropiate equality statements. And orbital mechanics, is it not orbital velocity that accounts for the altitude of a orbiting body. Is not escape velocity, dependant on the M of the object in question; along with its' velocity? I realize this comprises a departure from the basics of free-fall, and may furthar perplex my mind with conundrumisms, but all the same; an object that masses at 1000, as compared with one that has a mass of 250; should be more affected by an object the size of the Earth; and so, should exhibit a stronger attractive force with a significant gravitating body, such as the earth. Unless I'm to perplexed to think properly at this moment.

I have a better understand, yet I am still perplexed and waxing conundrum-ish.

Jeffrey

 

[TurtleMeister]

If A and B are equal in volume and mass they will hit the ground at the same time if they are not they won't.

He didn't say the masses were equal, just the volumes. In other words, the mass of A is much greater than the mass of B and the volume of A is equal to the volume of B.

You need to do Simon's experiment in two phases, once for mass A and then for mass B. You cannot work with three masses simultaneously using only simple math. You would need something like an n-body simulation program.

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?

 

[Simon Bridge]

Yes, from my understanding it is Mass that accounts for gravity.

It is not clear what that means - in Newtonian Gravitation, the strength of gravity is directly proportional to the product of the masses and inversely as the square of their separations. In the back of your mind you should have a caution that Newtonian physics is not all there is to it.

The Moon has a tidal force that is affecting Earth.

The tides are not a "force".
There is a lot written online about how the tides happen - you should read through them. Hint: it's not just about water.

is it not orbital velocity that accounts for the altitude of a orbiting body.

No, it isn't.

Is not escape velocity, dependent on the M of the object in question; along with its' velocity?

The escape velocity from a position in a gravitational field depends on the gravitational potential at that position, yes. Why would anyone expect any differently?

I realize this comprises a departure from the basics of free-fall,

The escape velocity is the minimum initial radial velocity needed, under free-fall conditions, to avoid falling back to the initial radial position. It is quite apropos to the subject.

an object that masses at 1000, as compared with one that has a mass of 250; should be more affected by an object the size of the Earth; and so, should exhibit a stronger attractive force with a significant gravitating body, such as the earth. Unless I'm to perplexed to think properly at this moment.

That is correct - it is because the force of gravity is greater, for the greater mass, that the acceleration is the same.

You still need to be more careful of your language ... for example: "the proper calibration to make the appropriate equality statements", does not seem to have any meaning that I can figure out. Calibration is appropriate to measuring instruments while "equality statements" would be appropriate to political science ... but, in context, maybe a reference to mathematical equations? Whatever, the two don't seem to depend on each other.

Keep your language simple and minimally adorned and people are more likely to understand you and you are more likely to understand what you are trying to describe.

You should also start expressing yourself more in terms of mathematics.
The more you do the math the more you will get the feel for the relations and what the different physics are telling you.

Lastly, a great part of Science is in giving up erroneous ideas when you discover them.
Have fun.

 

[jeffrey c mc.]

The Moon has a tidal force that is affecting Earth.

Here I am speaking of the tidal force of the Earth's Moon. I have read Astronomy content referring to the tidal forces of a Black Hole destroying objects that are misfortune enough to get too close.

That is correct - it is because the force of gravity is greater, for the greater mass, that the acceleration is the same.

Brain Freeze, have to get back on that, it makes my brain feel numb.

If the Moon had a M of 5g, how would that effect the bodies of water on the earth? Even if it was near enough to provide, the proper calibration to make the appropriate equality statements.

What I was trying to say here was if the moon was scaled down to 5g, and then moved closer to earth, so as a balance was made; or an equality, from being large and far away, to being small and much closer; would it have the same affect on the tides.

is it not orbital velocity that accounts for the altitude of a orbiting body.

I see my use of language has fallen short here, I presume. 'An object in stable orbit' would have; I think; cleared this statement up some. Once an object is in a stable orbit; then, in order to increase its' altitude above the object it is in stable orbit about, one; me, myself, and I; would presume that the only thing wanting would be a increase in its' orbital velocity.

Simon, thank you for your feedback. I do realize that I put the poor English language to task, and the only reason I can possibly learn why, is for individuals to take the time to try to parse the meaning. Also, I am not necessarily in the 'know' about how, and why others do not 'get' me, as they say; it's quite as mysterious to me as Newton's apple. Which, by the by, fell on his head a long time in the past; so your hint that there has been much elucidating on the topic since then, is quite on the money.

Thanks again
Jeffrey

 

[Simon Bridge]

Here I am speaking of the tidal force of the Earth's Moon. I have read Astronomy content referring to the tidal forces of a Black Hole destroying objects that are misfortune enough to get too close.

The mechanism that produces the ocean tides on the Earth is the same as tears objects apart close to black holes and pushes the Earth and Moon apart.
http://www.badastronomy.com/bad/misc/tides.html
http://www.jal.cc.il.us/~mikolajsawicki/ex_tides.html

Brain Freeze, have to get back on that, it makes my brain feel numb.

hint: acceleration and force are different things.
Have you seen the famous Apollo hammer/feather drop experiment?

What I was trying to say here was if the moon was scaled down to 5g, and then moved closer to earth, so as a balance was made; or an equality, from being large and far away, to being small and much closer; would it have the same affect on the tides.

No - the geometry would be totally different.
You should read more about how tides happen before pursuing this line of thought.

I see my use of language has fallen short here, I presume. 'An object in stable orbit' would have; I think; cleared this statement up some. Once an object is in a stable orbit; then, in order to increase its' altitude above the object it is in stable orbit about, one; me, myself, and I; would presume that the only thing wanting would be a increase in its' orbital velocity.

Firstly, it is key to your understanding here that one object does not orbit another - both objects orbit their common center of mass.

However, where one object is much more massive than the other, the common center of mass will be very close to the center of mass of the more massive object. It is in this sense that we talk about, say, satellites orbiting the Earth.

Secondly - a stable orbit, in a two-body system, is an ellipse (technically, any conic section will be stable but only ellipses and circles loop back and circles are not stable.) This means that, for any stable orbit, the orbital velocity is not a constant and nor is the distance from the primary.

In the ideal case of a circle, the orbital velocity is a constant and so is the orbit radius. The orbit may be changed by changing the orbital speed, or just changing the direction of the velocity (adding or removing a radial component, say).

One of the simplest ways to get from one circular orbit to another is to change to an elliptical orbit as an intermediate. You can look up "exchange orbit". There are a lot of other tricks and it is rocket science. Try to get used to the simple stuff first eh?

Simon, thank you for your feedback. I do realize that I put the poor English language to task, and the only reason I can possibly learn why, is for individuals to take the time to try to parse the meaning.

Technically you are using a form of English that is quite the opposite to poor but is not very useful to the task. Ironically, if your vocabulary were more lacking, you would have an easier time being understood.

But you have trained and worked, you have indicated, in a capacity which required a simpler and more direct way of writing so you should be able to handle it.

 

[jeffrey c mc.]

Thank you Simon for the excellent video. I wonder why these were not released for public consumption at the time. I do remember some of the early live televised programs, from grade school; perhaps they all were repressed due to the Auschwitz and Dachau documentaries, that were common for the education of the masses, about the same time. It would appear your discussion(s) in #25 are centered around Einstein-ian physics and beyond. Meaning since the man, of course. I've seen some of the 'graphic' thought behind that; yet, one conundrum becomes apparent with that. 'why only one dimple' in that I mean, should not the 'distortion' be 'mirrored;' only set at a flipped over; or at an antipodal; or, reversed; or an 180 degree shifted; aspect? I've seen the graphic; with the distortion; with the moon rolling about in the distortion; yet, it would seem it is missing the counterpart, there should be a twin of the distortion, set in an 180 degree divergent aspect. I suppose this goes into super-symmetry. But that's the kind of guy I am, a super-symmetrical, philosopher. Not a mechanic, or engineer; I gave that idea up when I realized someone who liked to use various intoxicating substances, had no business working on a commercial flight-line, or shop, repair, or otherwise. Who could have guessed.

Thanks for the links and pointers, I will be reviewing them later.

 

[Simon Bridge]

Thank you Simon for the excellent video. I wonder why these were not released for public consumption at the time.

I understand that this experiment was broadcast live in 1971. It's quite famous.

It would appear your discussion(s) in #25 are centered around Einstein-ian physics and beyond.

Whatever gave you that idea?
Everything in post #25 is Newtonian physics.

I've seen some of the 'graphic' thought behind that; yet, one conundrum becomes apparent with that. 'why only one dimple' in that I mean, should not the 'distortion' be 'mirrored;' only set at a flipped over; or at an antipodal; or, reversed; or an 180 degree shifted; aspect?

Nobody mentioned any dimples.
If you refer to the rubber-sheet analogy for General relativity, that is extensively discussed elsewhere.
Lets try to keep to one topic per thread?

But that's the kind of guy I am, a super-symmetrical, philosopher.

I don't think this actually means anything - please try to use words in a meaningful way. I know it's more fun being playful but it does make it difficult to help you.

There is a philosophical forum in PF as well if your inclinations got that way.
Please read the stickies and the faq.
Have fun :)

 

[Buckleymanor]

Is this what you are having a problem with? Do you think that this contradicts the universality of free fall?

Size seems to be the main problem with regards acceleration.
The Earth does not rush towards a falling bowling ball at 9.8 mtrs/sec.
However if the bowling ball was replaced with another Earth would it then rush towards it at that speed or twice as fast.

 

[jeffrey c mc.]

Buckley: The text you included in quote form does not appear in previous threads. Unless it's in a portion of a block paragraph which is excluded. I'm not responding more at this time until this question is reconciled. I'm also unclear if your supposition in the body text of thread with time stamp 3:10, refers to the quote, or, of a general nature, relating to previous threads.

Jeffrey

 

[Buckleymanor]

Buckley: The text you included in quote form does not appear in previous threads. Unless it's in a portion of a block paragraph which is excluded. I'm not responding more at this time until this question is reconciled. I'm also unclear if your supposition in the body text of thread with time stamp 3:10, refers to the quote, or, of a general nature, relating to previous threads.

Jeffrey

Try, post 22 last paragraph from TurtleMeister yesterday time stamp 10:39 pm.
The supposition I am trying to make is that acceleration due to gravity of all object's is dependent on the size of the object's mass.
Under "normall" conditions object's attracted by the Earth or Moons gravity seem to accelerate at the same rate.
Like with the hammer and feather on the Moon.
When the mass of the Moon or Earth is considered in comparrison to the mass of the hammer and feather this is hardly supriseing.
If the supposition that all things within a gravity field fall at the same rate then all objects including the Moon or Earth should also, which is clearly not the case when a hammer and feather is dropped on them.You have to remember that when you drop something towards Earth or the Moon
the Moon and Earth is attracted as much to the object you dropped as the object is attracted to them.
They in effect jump slightly towards the object but you don't feel or see it.
However if another Moon was dropped towards the Moon then this would be the case and they would accelerate at the same rate towards each other and you would see and feel it.Which shows it's dependent on the size of mass dropped.

 

[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.