Proof of the apple 'pulling' the earth?

[andbna]

You are like JR and have to explain how you know that gravity is a force... ...You seem to be saying gravity is a force because everyone says it’s a force. That is very much a psuedoscience answer.

Looks like James covered this well.

Not sure why you would say the gravitational field strength of the earth has not changed. Drop something under the moon. It falls at a slower rate to something dropped 6 hours further around the earth. The change is measurable. You are trying to say black isn't black for some reason or other.

It seems you completely ignored the fact that acceleration is dependant on the NET FORCE on an object, not the graviational field strength.
It only appears I'm saying black is not black is because you won't open your eyelids to look at the object.

You are presuming that the apple attracts the earth

Well I wouldnt be testing Newtons theories by assuming the apple does anything else, now would I?

Your trouble is you are seeing Z as a net force of zero. It is a resultant rate of acceleration of zero.

Ok good, now do some critical thinking and you can derrive that:
F=ma
F=m*0
0m=0
F=0

Or in plain english: When the acceleration of an object is 0, the net force acting upon the object is 0.
My argument still stands... And so does my nebulous one a page back, would you care to address it's points?

-Andrew

 

[plane]

plane:



You're arguing against yourself.

Take your point (1): gravity causes mass to accelerate. Newton's second law says what? Hmm... that's right. Here it is:

F = ma

On the right we have mass and acceleration. On the left, we have what causes that acceleration. What causes acceleration? Oh look! Force. And you know what? Nothing other than a force can cause a mass to accelerate. That's what we mean by "force". A force is something that causes an acceleration.

Therefore, we see by your own statement that gravity is a force.

I don't understand statement (2); it's not clear.



I'll be selective - just as you are selective in responding to my points. I notice that you won't engage with points you find inconvenient for your argument.

Do you have an open or closed mind about this?

No, my mind is very open. Would suggest that is what would lead someone to question whether an apple really does attract the earth.

Also I will engage in any point you want to that has to do with gravity. As long as you stick to it to an end point. This thread was started in an effort to find the considered proof of an apple attracting the earth. You tied your proof to gravity being a force. That is what I address.


Been able to see what you are saying.

Only force can cause acceleration thereforce gravity is a force. That is what you are saying.

What we know of gravity is that it is a mathematical construct in space. It is an inverse square law around mass.


Mathematical construct = force?

If gravity is a force, what is its equal and opposite when mass is not present at any point in the mathematical construct?

Yours to answer. Please don't make Newton's third law wrong.

Or in plain english: When the acceleration of an object is 0, the net force acting upon the object is 0.

Andrew, Z is not an object. It is a point in space. You've got get past seeing the necessity of a second object for gravity to exist.

Just think of a point in space 100,000 km from the earth. No mass is present. Is there gravity?

Then is there force? There is no m to give you a m.a so there is no force.

Thus ideas of gravity being a force are yours to substantiate. You can answer JR's equal and opposite question if you like.


I would really like proof along the lines of the large mass moving in a Cavendish experiment.

Intellectual arguments can hardly be expected to carry the day.

 

[temur]

There will be a point (actually a surface) between the two bodies where the net force is zero. This does not mean the force acting on both bodies will be zero (If your reasoning is correct you would imply not only the force acting on the big body is zero, the force on the smaller body is zero too, so there would be no gravitational interaction at all). You imagine moving from the middle (zero force) surface to the bigger body slowly. Then the gravitational force would increase from zero to some (vector) value pointing to the bigger body. When you approach the bigger body, the force will tend to infinity. But if you are standing EXACTLY on the bigger body, the force will be directed towards the smaller body. That is because exactly at the bigger body (assuming the body is pointlike), the gravitational force from itself is ZERO. This may sound strange but you can make it precise by considering locally supported distribution of mass. Generally in nonstatic situations gravitational force of a body acted on itself becomes nonzero.

 

[andbna]

You've got get past seeing the necessity of a second object for gravity to exist.

In order for there to be a force of gravity between two objects, there has to be 2 objects... a fairly obviouse fact.
That said, my proof works with or without an apple, devide one mass out of the equations and they still work (you will notice the functions do not change one bit, and what's more, an acceleration value is still given.)
This is because I measured the gravitational field strength at Z, which is the amount of acceleration any body will experiance at Z due to the gravitational effects. The net field strength is 0 at Z, however the strength of the earth an moon are still non-zero, all in accordance with Newton.
My argument stands.

What we know of gravity is that it is a mathematical construct in space. It is an inverse square law around mass.

False, we know that gravity exists, that it a scientific fact, don't believe me? Then fly away. Can't? Well then a force MUST be preventing you, this force is gravity. Newton modled it in mathmatical terms, and the function describing happens to be an inverse square.

If gravity is a force, what is its equal and opposite when mass is not present at any point in the mathematical construct?

When no second mass is present, there is no two objects presant for there to be a force between them, simple as that. The derived function when a second mass is not presant is the gravitational field strength which can predict the acceleration another mass would feel at a given point due to the first mass, you might have heard of the g constant? 9.8ms^-2 ? This is an approximation of the gravitational field stength of earth near it's surface.

Just think of a point in space 100,000 km from the earth. No mass is present. Is there gravity?

Then is there force? There is no m to give you a m.a so there is no force.

I would have thought the lack of force as being unmentionably obviouse, however Newton predicts the force of gravity to occur between 2 object, so there is no problem with his model. He does however predict a gravitational field strength for a given point, which describes the acceleration a body in that position would undergo. Perhaps you have heard of g=9.8ms^-2 the gravitational field strength of the earth at an arbitrary point near the surface of the earth? Please also note that this field strength is for one body, the actual acceleration felt will be the net field strength, calculated by adding the field strength of all bodies (this net value can be 0, the actual field strength of a single body cannot be.)

I would really like proof along the lines of the large mass moving in a Cavendish experiment.

Intellectual arguments can hardly be expected to carry the day.

Well, since your ignoring the cosmological amount of cosmological evidence, I'm afraid that's not possible. You see, masses manageable by humans create forces which are simply too small; the error of any test would be many times that of the resault, or expected resaults, themselves. Of course, if you can provide an experiment in which to test, which would produce a percent error of usable amounts, by all means share your ideas.

-Andrew

 

[James R]

plane:

Only force can cause acceleration thereforce gravity is a force. That is what you are saying.

What we know of gravity is that it is a mathematical construct in space. It is an inverse square law around mass.

Mathematical construct = force?

Now you're confusing the description of gravity with the physical reality of gravity. The physical reality of gravity is that when you drop an apple it falls to the ground (and the ground falls towards it, though that is much harder to see). The inverse square law quantifies how gravity changes with distance.

It is nonsense to say that gravity is "just a mathematical construct", if that is what you're claiming. It has real, observable, measurable effects.

If gravity is a force, what is its equal and opposite when mass is not present at any point in the mathematical construct?

I'm not sure what you're asking, but perhaps you're alluding to the gravitational field, as opposed to the gravitational force. Unlike the force, which is measurable, as a first approximation you can consider the field to be a pure mathematical construct. The gravitational field strength at a given point in space tells you what force would be experienced by a standard "test mass" if it were placed at that point. But the field is just a calculational convenience. It is the force that is real.

There is no Newton's Third Law for fields. Nothing in physics requires that every field has an equal and opposite field. Newton's third law only applies to force interactions between two objects. So, if you have only one object, Newton's third law is totally irrelevant.

Just think of a point in space 100,000 km from the earth. No mass is present. Is there gravity?

Observationally, there's no way to tell unless you put a mass at the point in space.

Theoretically, as a calculation convenience, we say that there is a gravitational field at the point in space, such that if you put a standard mass there it would feel a particular force.

Then is there force? There is no m to give you a m.a so there is no force.

Correct.

 

[plane]

There will be a point (actually a surface) between the two bodies where the net force is zero. This does not mean the force acting on both bodies will be zero (If your reasoning is correct you would imply not only the force acting on the big body is zero, the force on the smaller body is zero too, .

No Temur. Go through the thread. Look at the second diagram. Small gravity field within the large gravity

In order for there to be a force of gravity between two objects, there has to be 2 objects... a fairly obviouse fact.

If objects cause gravity and gravity is a force, why does there have to be a second object present for gravity to be a force.

That said, my proof works with or without an apple, devide one mass out of the equations and they still work (you will notice the functions do not change one bit, and what's more, an acceleration value is still given.)
This is because I measured the gravitational field strength at Z, which is the amount of acceleration any body will experiance at Z due to the gravitational effects. The net field strength is 0 at Z, however the strength of the earth an moon are still non-zero, all in accordance with Newton.
My argument stands.

Your argument does not stand. Stating however proves nothing.

How do the earth and moon gravities cause a net acceleration of zero and still exist whilst they do it.?

Do they cause the net result in once instance, then go back to their otherwise values in the next instance then cause the net result again etc. How can a net result and the causes of a net result co-exist. Physically and mathematically impossible. Please don’t take it to personally but it makes you look very weak when you insert however the way you do with nothing to back it up.

False, we know that gravity exists, that it a scientific fact, don't believe me? Then fly away. Can't? Well then a force MUST be preventing you, this force is gravity. Newton modled it in mathmatical terms, and the function describing happens to be an inverse square.

You are obviously scraping the bottom of the barrel a bit with your must in capitals. If that is your best ‘argument’, you better give up. What prevents me from flying away is my weight. My weight is a product of my mass and the earth’s gravity strength.

When no second mass is present, there is no two objects presant for there to be a force between them, simple as that. The derived function when a second mass is not presant is the gravitational field strength which can predict the acceleration another mass would feel at a given point due to the first mass, you might have heard of the g constant? 9.8ms^-2 ? This is an approximation of the gravitational field stength of earth near it's surface. .

So you are saying that gravity is not a force unless there are two masses present.. Doesn’t fit with your other logic of mass causes gravity and gravity is a force. Your second logic says gravity is a force because of one mass, not because of two masses.

I would have thought the lack of force as being unmentionably obviouse, however Newton predicts the force of gravity to occur between 2 object, so there is no problem with his model. He does however predict a gravitational field strength for a given point, which describes the acceleration a body in that position would undergo. Perhaps you have heard of g=9.8ms^-2 the gravitational field strength of the earth at an arbitrary point near the surface of the earth? Please also note that this field strength is for one body, the actual acceleration felt will be the net field strength, calculated by adding the field strength of all bodies (this net value can be 0, the actual field strength of a single body cannot be.)

Well, since your ignoring the cosmological amount of cosmological evidence, I'm afraid that's not possible. You see, masses manageable by humans create forces which are simply too small; the error of any test would be many times that of the resault, or expected resaults, themselves. Of course, if you can provide an experiment in which to test, which would produce a percent error of usable amounts, by all means share your ideas.

-Andrew

Reading your Newton predicts force of gravity to occur between two bodies, he doesn’t really. He predicts every particle “attracts” every other particle. Then goofs off into a formula only involving two particles.

Not ignoring cosmological evidence. The criss cross of the earth across its solar path in tune with the moon’s orbit of the earth is noted. This is evidence of the earth and moon as a whole moving away from the sun. Not evidence of the moon attracting the earth.

plane:



Now you're confusing the description of gravity with the physical reality of gravity. The physical reality of gravity is that when you drop an apple it falls to the ground (and the ground falls towards it, though that is much harder to see). The inverse square law quantifies how gravity changes with distance.

It is nonsense to say that gravity is "just a mathematical construct", if that is what you're claiming. It has real, observable, measurable effects. .

Confusing nothing. The mathematical construct has a real observable effect. Acceleration. Acceleration that decreases as an inverse square of distance moved away from the mass the construct is around. You have confessed to not knowing has mass causes gravity so probably wouldn’t hurt you to get a little deeper into this area if you have anything of a genuine interest in gravity.

Your notion seems to be that the potential for acceleration is not there unless a second mass is present. You aren't in the dark ages are you? Very much you seem like a pseudo scientist.

I'm not sure what you're asking, but perhaps you're alluding to the gravitational field, as opposed to the gravitational force. Unlike the force, which is measurable, as a first approximation you can consider the field to be a pure mathematical construct. The gravitational field strength at a given point in space tells you what force would be experienced by a standard "test mass" if it were placed at that point. But the field is just a calculational convenience. It is the force that is real. .

Refer to previous answer.

There is no Newton's Third Law for fields. Nothing in physics requires that every field has an equal and opposite field. Newton's third law only applies to force interactions between two objects. So, if you have only one object, Newton's third law is totally irrelevant. .

Your are supposed to be addressing what is the equal and opposite force to gravity if gravity is a force, as you claim it to be.

As an incidental, if gravity strength is proportional to quantity and if an apple did attract the earth, why would you multiply the apples quantity by the earth’s quantity to find a composite force.

If the apple and the earth did produce a composite force, would you not add their quantities if quantity and gravity strength are directly proportional.


So the question to answer for today is

If mass causes gravity and gravity is a force, where is the equal and opposite force to the force that mass is causing?

Hit the keyboards. Give it your best shot. Almost bet that no answer of sense will be forthcoming.

 

[temur]

I already said what is wrong with your point and you ignore it so I have no interest in coming back here again.

 

[andbna]

If objects cause gravity and gravity is a force, why does there have to be a second object present for gravity to be a force.

All forces are interactions between 2 objects, always.

How do the earth and moon gravities cause a net acceleration of zero and still exist whilst they do it.?

The exact nature of 'how' is irrelevant, the issue is that it does, and there is no law or logic which dictates that they cease to exist.
An analogy: A man is place on The Rack, one rope binds his arms and pulls up, the other to his legs pulling down. The man himself does not move, the net force on him is 0, however, he still feels the forces of each rope pulling in opposite directions; if the forces ceased to exist, the torture device would have been ineffective, however they do not.
As it turns out, gravity can cause a similar fictional force; the Tidal force. The apple, or whatever object, if placed at Z, would experience a force. One side attracted toward the moon, the other toward earth. While not significant at this scale, replace moon and earth with a binary neutron star system, and the tidal force at Z could be fatal.

How do the earth and moon gravities cause a net acceleration of zero and still exist whilst they do it.?

Once again, the 'how' is unimportant, your under the impression that there is a law which states that if 2 vectors add to 0, they must not exist. I have heard of no such thing.

Do they cause the net result in once instance, then go back to their otherwise values in the next instance then cause the net result again etc.

What do you mean by 'instance' ?

How can a net result and the causes of a net result co-exist.

There's nothing which prooves they cannot, and by all observations, they do. This is a question of philosophy, not science, to which I can ask "How can anything exist?"

Physically and mathematically impossible.

Proof?

What prevents me from flying away is my weight. My weight is a product of my mass and the earth’s gravity strength.

‘Gravity strength’ is not a defined term in physics. However weight is clearly defined as being proportional to mass and the gravitational field strength at a given location, obviously on earth, this is earth’s gravitational field strength, thus it is earth’s force of gravity acting upon you which prevents you from flying away.

So you are saying that gravity is not a force unless there are two masses present.. Doesn’t fit with your other logic of mass causes gravity and gravity is a force. Your second logic says gravity is a force because of one mass, not because of two masses.

Straw man argument. I stated that the force of gravity only exists as an interaction between two masses. This applies to all forces, for example electromagnetic.

Reading your Newton predicts force of gravity to occur between two bodies, he doesn’t really. He predicts every particle “attracts” every other particle.

Seriously? If there wasn't another particle to attract, and therefore another mass, then there would be no gravity, now would there?

Then goofs off into a formula only involving two particles.

Perhaps because 2 particles is the simplest problem to which his theory can be applied to, from which, the interaction between multiple particles can be computed?

As an incidental, if gravity strength is proportional to quantity and if an apple did attract the earth, why would you multiply the apples quantity by the earth’s quantity to find a composite force.

If the apple and the earth did produce a composite force, would you not add their quantities if quantity and gravity strength are directly proportional.

Because if x and y are proportional to z, then z=xy, that is what the word 'proportional' signifies when used in a mathematical context.

Your are supposed to be addressing what is the equal and opposite force to gravity if gravity is a force, as you claim it to be.

If mass causes gravity and gravity is a force, where is the equal and opposite force to the force that mass is causing?

Hit the keyboards. Give it your best shot. Almost bet that no answer of sense will be forthcoming.

"The earth pulls on the apple (Fg earth on apple) and the apple pulls back on the earth (with equal and opposite strength, Fg apple on earth, is the reaction force.)"
Perhaps you expect the reaction force to be of a different nature than the action force? It is rather, always of the same nature.

...it makes you look very weak when you insert however the way you do with nothing to back it up.

You are obviously scraping the bottom of the barrel a bit with your must in capitals.

If that is your best ‘argument’, you better give up.

You have confessed to not knowing has mass causes gravity so probably wouldn’t hurt you to get a little deeper into this area if you have anything of a genuine interest in gravity.

You aren't in the dark ages are you? Very much you seem like a pseudo scientist.

Arguments ad hominem.

-Andrew

 

[James R]

plane:

If we're not going to have an honest conversation, then you're wasting my time. You're going to need to start addressing all the points I make, and not ignoring the ones that are inconvenient for you.

Your notion seems to be that the potential for acceleration is not there unless a second mass is present. You aren't in the dark ages are you? Very much you seem like a pseudo scientist.

This is the kind of dishonesty I'm talking about. You slip in the word "potential", but you must realise that there is a difference between an actual acceleration and a "potential for acceleration". In fact, I tried to carefully educate you on the difference between force and field in my previous post, but you conveniently ignore what you learned there in making the above statement. This suggests to me either that you're stupid and really can't understand explanations, or that you're dishonest and want to stick your fingers in your ears and pretend not to hear things you don't like the sound of.

Making accusations that I am a pseudoscientist makes you look even more on the fringe than how you started. The only things I have told you are what standard physics, accepted by all professionals in the field, says.

As an incidental, if gravity strength is proportional to quantity and if an apple did attract the earth, why would you multiply the apples quantity by the earth’s quantity to find a composite force.

It's a simple matter of logical deduction. Take two masses, 1 kg and 1 kg. Measure the gravitational force exerted by one on the other at a given distance. Now, replace one of them by a mass twice as large, 2 kg. Measure the force again. It is twice as large. So, we conclude that the force depends on the product of the masses. It cannot, for example, depend on the sum of the masses.

If the apple and the earth did produce a composite force, would you not add their quantities if quantity and gravity strength are directly proportional.

No. In my example, if we added the masses, then in the second case there would be a total of 3 kg, as opposed to an initial 2 kg total, so we'd expect an increase in the force by a factor of 3/2. Instead, we observe a doubling of the force.

So, your hypothesis is easily disproved.

If mass causes gravity and gravity is a force, where is the equal and opposite force to the force that mass is causing?

If mass A exerts a gravitational force on mass B (remember, two masses are required, since all forces are interactions), then B exerts a force of equal magnitude on A, in the opposite direction. This is Newton's third law.

Hit the books. Give it your best shot. Who knows? Maybe even you will be able to learn the basic laws of motion if you try.

 

[plane]

Andrew don’t know how you type this. No point going around in circles with the rest of it but this

Seriously? If there wasn't another particle to attract, and therefore another mass, then there would be no gravity, now would there.

You jest. You are saying if only mass existed in the universe, that mass would have no gravity?

Because if x and y are proportional to z, then z=xy, that is what the word 'proportional' signifies when used in a mathematical context.

X and y and not proportional to z. Mass is proportional to gravity strength. Not mass x mass is proportional to gravity strength.

plane:





This is the kind of dishonesty I'm talking about. You slip in the word "potential", but you must realise that there is a difference between an actual acceleration and a "potential for acceleration". In fact, I tried to carefully educate you on the difference between force and field in my previous post, but you conveniently ignore what you learned there in making the above statement. This suggests to me either that you're stupid and really can't understand explanations, or that you're dishonest and want to stick your fingers in your ears and pretend not to hear things you don't like the sound of..

You just don’t get my point. I guess that is my fault. To a certain extent anyway. By potential I mean that a rate of acceleration exists in space whether or not an object is present and all I am doing, anyway, is trying to follow your logic. You say gravity is a force. And this is proof of an apple attracts the earth.

My "proof" is:

1. Newton's third law states that for every force there is an equal and opposite force.
2. Therefore, when two bodies interact, if one exerts a force F on the other, the other exerts an equal force F on the first, but in the opposite direction.
3. Gravity is a force (in the Newtonian picture).
4. No known experiment with force has ever violated Newton's third law.
5. Therefore, if the Earth pulls on an apple, the apple must pull back on the Earth with an equal and opposite force.

And then you posted that gravity is a force because physics say so. I pointed out what we know about gravity with respect of 3 but perhaps we better go back to2. Your proof I suppose is fundamentally dependent on the ‘if’ in 2.

You presume the red arrow is a force. How is it applied to the apple?

Making accusations that I am a pseudoscientist makes you look even more on the fringe than how you started. The only things I have told you are what standard physics, accepted by all professionals in the field, says.

I have told you before, everyone accepting that something is right doesn’t make it right. Professional scholars once accepted that the earth is the centre of the universe. If you think your a genuine scientists, nothing I post should change that.

It's a simple matter of logical deduction. Take two masses, 1 kg and 1 kg. Measure the gravitational force exerted by one on the other at a given distance. Now, replace one of them by a mass twice as large, 2 kg. Measure the force again. It is twice as large. So, we conclude that the force depends on the product of the masses. It cannot, for example, depend on the sum of the masses.



No. In my example, if we added the masses, then in the second case there would be a total of 3 kg, as opposed to an initial 2 kg total, so we'd expect an increase in the force by a factor of 3/2. Instead, we observe a doubling of the force.

So, your hypothesis is easily disproved.

Really. Didn't even think I put a hypothesis up. Just asked a question.

Your conclusion aside all you do is state that mass is proportional to a rate of acceleration due to gravity..

What I mean is this.

We have two masses. One 2 kg and the other 5kg. They are separated by a certain distance. F = G x 5 x 2/ d x d. So we have 7 kgs producing a gravitational force that equals 10.

Now we rearrange the masses and take 1kg from the larger mass and attach it the smaller. In a Cavendish type situation if you like. We don’t alter d.

Now we have F = G x 4 x 3/d x d. So now, according to the Cambridge scholar of yesterday year, we have 7 kgs of mass producing a graviational force that equals 12.

And yet gravity strength is proportional to quantity.

How does the gravitational force increase from 10 to 12 after some of one mass is transferred to the other?

To me that is an important consideration to be addressed before I hitch my wagon to an apple ‘attracting’ the earth in accordance with Newton’s law of gravity.

Of course you will come up with a glib answer to make this consideration irrelevant.

Incidentally, have pointed out in this thread that the small masses are always cancelled out during the calculation of G in Cavendish experiments. And that the experiments only confirm a relationship between the quantity of the large mass and its gravity strength.

Sorry for wasting your time but anyone with a questioning mind can only exercise doubt about an apple attracting the earth.

 

[James R]

plane:

You just don’t get my point. I guess that is my fault. To a certain extent anyway. By potential I mean that a rate of acceleration exists in space whether or not an object is present...

To measure a "rate of acceleration" you need something to be accelerating.

But maybe you're just talking about the field again, without being specific. Do you understand the distinction between force and field?

My "proof" is:

1. Newton's third law states that for every force there is an equal and opposite force.
2. Therefore, when two bodies interact, if one exerts a force F on the other, the other exerts an equal force F on the first, but in the opposite direction.
3. Gravity is a force (in the Newtonian picture).
4. No known experiment with force has ever violated Newton's third law.
5. Therefore, if the Earth pulls on an apple, the apple must pull back on the Earth with an equal and opposite force.

And then you posted that gravity is a force because physics say so.

The term "force" is defined to anything that causes an object to accelerate. If you agree that gravity causes objects to accelerate, then gravity is a force.

If you wish to redefine the word "force", please tell me what your own idiosyncratic definition is. All I've told you is how physicists define it. If your definition is different, then we're talking at cross purposes and the discussion will go nowhere. We need to agree on what "force" is, before we can even being to discuss gravity in any meaningful way.

You presume the red arrow is a force. How is it applied to the apple?

It's action at a distance. Quite clearly, gravitational forces do not require direct contact between objects.

I have told you before, everyone accepting that something is right doesn’t make it right. Professional scholars once accepted that the earth is the centre of the universe. If you think your a genuine scientists, nothing I post should change that.

Don't worry about me. I'm quite content in what I believe about myself, I assure you.

What I mean is this.

We have two masses. One 2 kg and the other 5kg. They are separated by a certain distance. F = G x 5 x 2/ d x d. So we have 7 kgs producing a gravitational force that equals 10.

Now we rearrange the masses and take 1kg from the larger mass and attach it the smaller. In a Cavendish type situation if you like. We don’t alter d.

Now we have F = G x 4 x 3/d x d. So now, according to the Cambridge scholar of yesterday year, we have 7 kgs of mass producing a graviational force that equals 12.

And yet gravity strength is proportional to quantity.

This may help us make some progress.

Probably, your misconception lies in the last sentence quoted here. You assume, for reasons that are unclear, that "gravity strength is proportional to quantity", by which I assume you mean that the force between two objects is proportional to the total mass of the two objects combined.

There's a problem. The formula F=GMm/r^2 gives the magnitude of the force on one object (either M or m), and not some kind of "shared" force that applies to both objects. To make this clearer, let's consider the acceleration of one of the two objects instead of the force. Take object M to be the one creating the force (for example, M is the Earth), and object m to be the one experiencing the force. Now, according to Newton's second law, the acceleration of m is:

a = F/m

And, the force on m is

F = GMm/r^2.

Therefore, the acceleration of m is:

a = GM/r^2.

Notice that the acceleration of m is determined by its distance from M and the magnitude of M only. The mass of m itself does not enter the equation.

Now, look again at your example. Let's take M=5 kg and m=2 kg, as in your first situation. The acceleration of the 2 kg mass towards the 5 kg mass is then

a = G(5)/r^2

In your second situation, you have M=4 kg and m=3 kg. The acceleration of m is now:

a = G(4)/r^2

It's less than before. But that makes sense, because there's now less mass "pulling" it. Whereas before a mass of 5 kg was attracting it gravitationally, now there's only a mass of 4 kg attracting it. Hence, less acceleration.

While we're at it, consider the acceleration of the larger mass in the two situations. Before the mass change, the acceleration of the 5 kg mass towards the 2 kg mass is

A = G(2)/r^2

Afterwards, it is

A = G(3)/r^2

So, the acceleration of the larger mass towards the smaller one increased, while the acceleration of the smaller mass decreased, as we would expect.

The important thing to take away from this is that the acceleration of one object is determined only by the mass of the other.

But...

How does the gravitational force increase from 10 to 12 after some of one mass is transferred to the other?

It increases because the effect of mass is multiplicative, not additive. There's really little else that can be said about this. It's an experimentally confirmed fact about how gravity works. Sure, you may be able to imagine a world in which gravity didn't work like that, but it's just not our world. Like it or not, you have to live with it. We can't dictate to nature how she works.

 

[plane]

plane:



To measure a "rate of acceleration" you need something to be accelerating.

Not really. You can use the inverse square law to calculate what a rate of acceleration in space would be.

The term "force" is defined to anything that causes an object to accelerate. If you agree that gravity causes objects to accelerate, then gravity is a force.



If you wish to redefine the word "force", please tell me what your own idiosyncratic definition is. All I've told you is how physicists define it. If your definition is different, then we're talking at cross purposes and the discussion will go nowhere. We need to agree on what "force" is, before we can even being to discuss gravity in any meaningful way.

Well I have posted my definition several times if you have been following. Force is the exertion of matter upon matter.

It's action at a distance. Quite clearly, gravitational forces do not require direct contact between objects.

How is an action at a distance applied? Do you know?

There's a problem. The formula F=GMm/r^2 gives the magnitude of the force on one object (either M or m), and not some kind of "shared" force that applies to both objects. To make this clearer, let's consider the acceleration of one of the two objects instead of the force. Take object M to be the one creating the force (for example, M is the Earth), and object m to be the one experiencing the force. Now, according to Newton's second law, the acceleration of m is:

Not sure why you can’t see it. Newton’s law of gravity specifically says that both masses create the force.

Every particle in the universe attracts every other particle in the universe with a force that is proportional to the product of their masses

etc.

The force is proportional to the product of their masses.

You multiply the masses together to find the force. That’s the what the law states.

When you go setting mg equal to G.M.m/d x d (mg = G.M.m/d x d) on the left hand side you have the force m experiences courtesy of the large Mass.

On the right hand side you have a force that supposedly is a force that M and m jointly create (once again the product of their masses).

a = F/m

And, the force on m is

F = GMm/r^2.

This what you have to answer,JR

How does m cause the force on its self? You might notice you have the small mass in your second equation.

Therefore, the acceleration of m is:

a = GM/r^2.

Which is just the inverse square law and an expression of the gravity strength of a body (M in this case) being proportional to its quantity. Refer you to the forst post in this thread.

You can see that you are saying the small mass is causing a force on its self can’t you?

Not much point going through the rest of your post unless you can see that. I have put it in bold back up the page a bit for you but everything I posted about 5 kg and 2 kg and 3 kg and 4 kg masses is consistent with

Every particle in the universe attracts every other particle in the universe with a force that is proportional to the product of their masses

Your reply was at odds with it. Somehow I feel sorry for you.

 

[plane]

For good measure

This law does not make a distinction between M and m. Swap the positions of the two masses and the magnitude of the force is the same.

Take object M to be the one creating the force (for example, M is the Earth), and object m to be the one experiencing the force.

JR the first is what you posted in post 14. The second is what you posted in post 71.

Initially you say M and m are necessary to F. Swap the positions of M and m and the magnitude of the force is still the same. Can only mean both masses create the force.

Later you move to one of the masses being the force creator. If what you post in post 71 is true

Take object M to be the one creating the force

gravity can hardly be said to be proven to be universal by you.

If you have the intellectual integrity you seem to pride your self in, you can see you have work to do to get your self sensible.



And you can see that I am well within my rights to call you a pseudo scientists if you vacillate between M and m causing the force and M only causing the force. Any 15 year old would be uncertain of just where you are at from what you are posting. Is it M or is it M and m. Cheers.

 

[James R]

plane:

You can use the inverse square law to calculate what a rate of acceleration in space would be.

Yes. That value is called the gravitational field magnitude, as I explained earlier.

Well I have posted my definition several times if you have been following. Force is the exertion of matter upon matter.

That's so vague as to be unusable as a definition.

How is an action at a distance applied? Do you know?

Well, yes, I do, but it isn't relevant to the present conversation. I'm not about to launch into a discussion of quantum field theories here. You're still back at the stage of wondering what a force is.

Not sure why you can’t see it. Newton’s law of gravity specifically says that both masses create the force.

No, it doesn't. But we're splitting hairs here.

What Newton's law of gravity says is that the force experienced by one mass due to the presence of another depends on the product of the two masses. It does not talk about which mass "creates" the force at all.

We can have a semantic argument about this if you like, but it is peripheral to the issue.

If we go back to Newton's third law, it says that every action (force) has an equal an opposite reaction (force). But it says NOTHING about which force is the "action" and which is the "reaction". Both forces are, in fact, on an even footing. One force doesn't "cause" the other. Both result from an interaction.

When you go setting mg equal to G.M.m/d x d (mg = G.M.m/d x d) on the left hand side you have the force m experiences courtesy of the large Mass.

That's what I said.

How does m cause the force on its self?

This is a meaningless semantic question again. M and m interact gravitationally, such that each experiences a force of the same magnitude. Take away either one of the two masses and the other experiences no force. So, both masses are required for a force to exist on either of them.

You cannot say that only one of the masses "causes" the force. The force only exists when there are two masses.

Not much point going through the rest of your post unless you can see that. I have put it in bold back up the page a bit for you but everything I posted about 5 kg and 2 kg and 3 kg and 4 kg masses is consistent with

Every particle in the universe attracts every other particle in the universe with a force that is proportional to the product of their masses

No. Your conjecture is consistent with

"Every particle in the universe attracts every other particle in the universe with a force that is proportional to the sum of their masses"

This is false. This is where you went wrong.

Initially you say M and m are necessary to F. Swap the positions of M and m and the magnitude of the force is still the same. Can only mean both masses create the force.

Later you move to one of the masses being the force creator.

I will be more careful with my use of language in future posts. Clearly, you are easily confused.

 

[andbna]

It seems like the original problem is getting 'cloudy,' especialy since the majority of these rescent posts are semantic based, or misunderstandings.
To restate one proof of "the apple pulling the earth:"

1.The apple's momentum is increasing in the direction of the earth.

2. The law of conservation of momentum states that the momentum of a system must stay constant, unless acted upon by an outside force. This has never been falsified to my knowlege.

3. There is no outside force of the apple-earth system.

4. Thus, in the apple-earth system, in order for the apple to gain momentum in the direction of the earth, the earth must gain an equal, though opposite amount of momentum.

Gravity, nor forces, need not even enter the picture.
Simple as that.

-Andrew

 

[plane]

JR is this what you see when you see 'universal' gravitation? Cheers

 

[James R]

plane:

I see no problem with that.

If you don't like the force explanation, by the way, then andbna's explanation is another good alternative (although actually conservation of momentum is equivalent in content to Newton's third law, which brings us back to forces by a roundabout route).

There are many different ways to see that the apple must attract the Earth, or else it would violate numerous well-tested physical laws that are not restricted to applications involving gravity.

If you think the apple does not attract the Earth, then really you need to refute Newton's third law.

 

[plane]

If you think the apple does not attract the Earth, then really you need to refute Newton's third law.

No, not refute Newton’s third law at all. Something I would never want to do. It more or less explains existence. However Newton’s third law might be subject to a wrong application with respect of Newton’s law of gravity. We’ll see.

So next I presume you are saying that Newton developed his law of gravity through his second law.

On the left side of the diagram 4 is the quantity of mass in question and 10/d x d is a measure of the acceleration due to gravity that the 4 mass is subject to.

A mass of 10 would produce a certain rate of acceleration at the distance of the surface from it s centre.

Then the rate of acceleration towards the centre of the 10 mass at the 4 mass would be found by 10/d x d



Do you have any trouble with that?

Cheers.

 

[James R]

plane:

That's approximately correct, except where you put the k. (Actually, it's usually written G.)

The acceleration of gravity at distance d from the 10 kg mass is

$$a = \frac{G(10)}{d^2}$$

The force on the 4 kg mass is then

$$F = ma = (4)a$$

where a is as above.

If you want to find the force on the 10 kg mass, just swap the 4 and the 10 in the above equations.

 

[plane]

plane:


The acceleration of gravity at distance d from the 10 kg mass is

Having a hard drive problem, can't put a diagram up but wouldn't mind knowing what someone believes acceleration of gravity