Proof of the apple 'pulling' the earth?

[plane]

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.

1/ What is the acceleration of gravity? (acceleration due to gravity?) That reads as if gravity its self is accelerating.

2/ How does the magnitude of a force applied to a mass involve the mass its self.

The force on the 4 kg mass is then

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

Makes no sense. Take the apple on the ground or hanging from a branch. You should be able to see that Newton has taken the mass of the apple, multiplied the mass by the rate of acceleration caused by the earth's gravity and then said this is the force the apple applies to the ground or the branch.

When you use $$F = ma = (4)a$$ all you are finding is the weight of the 4 mass if it isn't moving towards the 10 mass.

That is sort of where your juxtaposed conclusion that gravity is a force because anything that causes acceleration is a force breaks down.

When mass is not moving towards a centre of gravity, it is not accelerating.

I am in the process of getting a new computer and haven't the software on this one to do a diagram to show precisely what I am getting at, but will do so within a week or so if all goes well with the delivery.

However, you should be able to see that here you are saying the force of gravity applied to mass is dependent on the quantity of the mass subject to the gravity in accordance with Newton's second law.

In other places you say the force is dependent on the force this mass places on another mass in accordance with Newton's third law.

Which is it?

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

This says that mass provides an acceleration towards its self at a certain rate at a certain distance from its self.

There is no second mass involved. Says nothing more than gravity is a rate of acceleration towards mass. Also does not say that gravity is a force.

Says that gravity exists whether or not a second mass is present. And that is what my whole treatment of gravity is based upon. (yet I am the pseudo scientist)

where a is as above.

So now every particle in the universe attracts every other particle in the universe with a force that is proportional to the mass of the particle being attracted.

Sounds rather like nothing less or more that Newton's second law when you recognize $$a = \frac{G(10)}{d^2}$$ as a tool for measuring potential rate of change of momentum.

Newton has probably become besotted by the way Galileo's shift from Aristotle ( F = mv to F = ma) mirrored when he set up things in a way I have done with the 4 and 10 mass diagrams.

From there has apparently forgotten that saying k.m.a = G.M.m/d x d is saying k.m.a = k.m.a


Obviously he has had an excited moment but more to the point, he has missed considering what happens when the opposite directions
$$a = \frac{G(10)}{d^2}$$ and
$$a = \frac{G(4)}{d^2}$$ meet before respectively they reach the 4 and the 10 mass.





Cheers.

 

[tablariddim]

Newton'a law of gravity has three elements to it.

1/ The inverse square law

2/ A direct proportion between mass and gravity strength

3/ Every particle attracting every other particle.

All that from one falling fucking apple...fucking hell, I should have paid attention to physics at school!

 

[James R]

plane:

1/ What is the acceleration of gravity? (acceleration due to gravity?) That reads as if gravity its self is accelerating.

I already carefully explained this to you in a previous post.

When we say "acceleration due to gravity" at a particular point in space, we are saying that if a mass is placed at that point it will accelerate at that rate. It's just short-hand.

Do you understand the distinction between force and field?

2/ How does the magnitude of a force applied to a mass involve the mass its self.

I already explained that to you.

Makes no sense. Take the apple on the ground or hanging from a branch. You should be able to see that Newton has taken the mass of the apple, multiplied the mass by the rate of acceleration caused by the earth's gravity and then said this is the force the apple applies to the ground or the branch.

Well, technically, in that case Newton would be first calculating the force on the apple. Then, using Newton's third law, he would deduce that the apple exerts an equal and opposite force on the Earth.

When you use $$F = ma = (4)a$$ all you are finding is the weight of the 4 mass if it isn't moving towards the 10 mass.

It doesn't matter whether it is moving towards the 10 mass or not. It's weight is the same.

When mass is not moving towards a centre of gravity, it is not accelerating.

Correct. And in that case it must have at least two forces on it - its weight (due to gravity) and some other force preventing it from falling.

However, you should be able to see that here you are saying the force of gravity applied to mass is dependent on the quantity of the mass subject to the gravity in accordance with Newton's second law.

Technically, this is in accordance with Newton's law of gravity, and not a direct application of Newton's second law. Newton's law of gravity is an independent empirical deduction, compared to Newton's second law.

In other places you say the force is dependent on the force this mass places on another mass in accordance with Newton's third law.

Which is it?

Both. Newton's second law and Newton's third law are independent of one another. One cannot be derived from the other.

This says that mass provides an acceleration towards its self at a certain rate at a certain distance from its self.

There is no second mass involved. Says nothing more than gravity is a rate of acceleration towards mass. Also does not say that gravity is a force.

Do you understand the difference between force and field?

So now every particle in the universe attracts every other particle in the universe with a force that is proportional to the mass of the particle being attracted.

Correct. That is an empirical fact.

Newton has probably become besotted by the way Galileo's shift from Aristotle ( F = mv to F = ma) mirrored when he set up things in a way I have done with the 4 and 10 mass diagrams.

It is another empirical fact that F=mv is incorrect. You don't even need to look at gravity to disprove F=mv.

From there has apparently forgotten that saying k.m.a = G.M.m/d x d is saying k.m.a = k.m.a

You seem to think that Newton's law of gravity and Newton's second law of motion are two ways of saying the same thing. They are not. They are independent statements about different things.

Obviously he has had an excited moment but more to the point, he has missed considering what happens when the opposite directions
$$a = \frac{G(10)}{d^2}$$ and
$$a = \frac{G(4)}{d^2}$$ meet before respectively they reach the 4 and the 10 mass.

Correct. Are you aware of the principle of superposition of forces?

 

[plane]

plane:



I already carefully explained this to you in a previous post.

When we say "acceleration due to gravity" at a particular point in space, we are saying that if a mass is placed at that point it will accelerate at that rate. It's just short-hand.

Do you understand the distinction between force and field?

So try again.

You introduced the phrase “acceleration of gravity”. I inquired as to whether or not you meant “acceleration due to gravity”.

Your reply is not in keeping with the inquiry.

I already explained that to you.

Didn’t. This was your answer.

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.

As you can see this is not consistent with

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

Take M to be the one creating the force/ you cannot say only one of the masses causes the force. At that point I elected to introduce the 10 - 4 diagram to try and get to the bottom of what you actually believe. As already explained, am without ability to do diagrams at the moment but as you can well see you lack coherency from page to page of this thread.

It doesn't matter whether it is moving towards the 10 mass or not. It's weight is the same.

Think you mean its mass is the same. A free falling body is weightless.

Technically, this is in accordance with Newton's law of gravity, and not a direct application of Newton's second law. Newton's law of gravity is an independent empirical deduction, compared to Newton's second law.

This is where you completely lose me. Go back to the diagram in post 78 and your reply in post 79. Your answer says nothing but Newton’s law of gravity was deduced from Newton’s second law. You are all over the shop. There is nothing clear and consistent coming through.

Do you understand the difference between force and field?

The point I have consistently made is the field causes a mass within the field to either have a momentum change or become a weight (force) directed towards the centre of the field.

So now every particle in the universe attracts every other particle in the universe with a force that is proportional to the mass of the particle being attracted.

Correct. That is an empirical fact.

You’re doing it again. You are saying the force applied to m is dependent on the magnitude of m.

Like saying the force a bat applies to a ball is dependent on the mass of the ball.

A bigger ball (in terms of mass) will require a greater force relative to a smaller ball to be accelerated at the same rate.

But basically, get a bigger faster bat, more force applied to any sized ball.

It is another empirical fact that F=mv is incorrect. You don't even need to look at gravity to disprove F=mv.

Irrelevant answer to the point made.

Correct. Are you aware of the principle of superposition of forces?

Thanks for agreeing that Newton didn't investigate what happens where opposite directions of a field meet. Such is irrelevant to the super position of forces.

Cheers.

 

[AlphaNumeric]

I haven't bothered to read the entire thread but the gist of it is plane denying that the Moon attracts the Earth but only vice versa, rather than the mainstream view which is they attract one another.

How then does plane explain the effect the Moon has on the Earth. We see the tides and it's been measured by laser ranging that the surface of the Earth's crust actually rises and falls about 30cm each day (as well as the tides) due to the Moons effect.

The Earth and the Moon orbit a common centre of mass (which is just below the Earth's surface if I remember correctly), not the Moon orbiting the dead centre of the Earth. This is a measured fact by satellites.

This essentially just the Earth/Moon version of the stellar wobble seen in distant stars with huge planets going around them.

PS I love how plane was totally oblivious to Ben's sarcastic "You're right". :lol:

 

[James R]

plane:

You seem to be playing dumb, by homing in on what you apparently think are inconsistencies in the statements I have made, while at the same time ignoring the information that has been patiently given to you.

Still, as I said, I will try to explain things more carefully to you, since you seem to have trouble grasping things (whether this be innocent ignorance on your part or a wilful attempt at obfuscation).

You introduced the phrase “acceleration of gravity”. I inquired as to whether or not you meant “acceleration due to gravity”.

The wording is unimportant. We talked about meaningless semantics previously.

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.

As you can see this is not consistent with

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

Take M to be the one creating the force/ you cannot say only one of the masses causes the force. At that point I elected to introduce the 10 - 4 diagram to try and get to the bottom of what you actually believe. As already explained, am without ability to do diagrams at the moment but as you can well see you lack coherency from page to page of this thread.

Your problem here comes back to Newton's third law again.

Newton's third law implies that ALL forces arise from interactions between two objects. Each object exerts a force of the same magnitude on the other, but the forces are oppositely directed. This is as true for a baseball hitting a bat as it is for an apple attracting the Earth gravitationally. This was the gist of my first quoted statement, above.

My second statement involves Newton's law of gravity. It allows us to calculate the magnitude of the gravitational force on either of two objects (mass M and mass m). The direction of that force will be opposite for each of the objects, but the magnitude is the same for both - a fact that is in total agreement with Newton's third law.

My statement that the law of gravity gives the force on one object has to do with the interpretation of that law, including the directional information. It also has to do with the definition of the term "force" itself. I was trying to make clear to you that a force, by definition, only ever acts on one object. When we talk about "a force", we always mean a force that is "caused" by one object and acts on another. So, for example, I can talk about the "force on an apple due to the Earth" or the "force on the Earth due to the apple". In this example, there are two forces. One acts on the apple, one acts on the Earth. As it happens, the two forces have the same magnitude in this case, but opposite directions. In technical terms, they form what is known as an action-reaction pair of forces, in the terminology of Newton's third law.

So, when I wrote this:

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

I was merely indicating to you that I wished to select out mass m as the object being acted upon and mass M as the object causing the action. Why? Because I wished to look at the acceleration of mass m, and to determine that I needed to look at the force on mass m only. There is, of course, an equal and opposite force on mass M due to mass m, but for the purpose of my discussion at the time, I did not wish to consider that.

I hope this clears up your misunderstanding of this simple issue. I really can't be much clearer.

Think you mean its mass is the same. A free falling body is weightless.

That depends on how you define "weight". For clarity, let me tell you how I define it. I define the weight of an object to be the gravitational force exerted on it. Using this definition, a free-falling object is not weightless.

There is, however, no universally agreed definition of "weight". Some physicists prefer to define weight as what a scale would measure. I prefer to call that "apparent weight". For an object in free fall, a scale will read zero, and so the object has no apparent weight. But it still has weight, according to my definition.

I hope this also clears up any confusion you have on this point. Having explained how I am using the word "weight", we will now be on the same page.

This is where you completely lose me. Go back to the diagram in post 78 and your reply in post 79. Your answer says nothing but Newton’s law of gravity was deduced from Newton’s second law. You are all over the shop. There is nothing clear and consistent coming through.

Newton's second law contains nothing about the inverse-square nature of Newton's law of gravity. This alone ought to make it clear to you that the law of gravity cannot be deduced from Newton's second law. On the other hand, Newton's method of arriving at the law of gravity involved a process both of induction from observation and deduction using his other knowledge of the laws of motion. Perhaps this confused you.

You’re doing it again. You are saying the force applied to m is dependent on the magnitude of m.

That is true for gravitational forces, according to Newton's law of gravitation. Just look at the equation if you're in any doubt.

Like saying the force a bat applies to a ball is dependent on the mass of the ball.

A bigger ball (in terms of mass) will require a greater force relative to a smaller ball to be accelerated at the same rate.

But basically, get a bigger faster bat, more force applied to any sized ball.

You're mixing all kinds of concepts here.

When a bat hits a ball, then according to Newton's third law, both the bat and the ball experience forces of equal magnitude and opposite directions. The bat exerts a force on the ball; the ball exerts a force on the bat. If you do not believe that the ball exerts a force on the bat, you need to explain why you can feel the ball hitting the bat, though the handle.

If the force exerted by the bat on the ball is F, then the acceleration of the ball is

a = F/m

where m is the mass of the ball. So, what you said about the effect of the mass of the ball is correct. Bigger m requires more F for the same acceleration.

You may well be able to apply more force if you get a more massive bat, or swing it faster. I am puzzled as to how you think this is relevant to gravity.

Thanks for agreeing that Newton didn't investigate what happens where opposite directions of a field meet. Such is irrelevant to the super position of forces.

Ok. If it's irrelevant, I won't worry about addressing it.

 

[plane]

I haven't bothered to read the entire thread but the gist of it is plane denying that the Moon attracts the Earth but only vice versa, rather than the mainstream view which is they attract one another.

How then does plane explain the effect the Moon has on the Earth. We see the tides and it's been measured by laser ranging that the surface of the Earth's crust actually rises and falls about 30cm each day (as well as the tides) due to the Moons effect.

The Earth and the Moon orbit a common centre of mass (which is just below the Earth's surface if I remember correctly), not the Moon orbiting the dead centre of the Earth. This is a measured fact by satellites.

This essentially just the Earth/Moon version of the stellar wobble seen in distant stars with huge planets going around them.

PS I love how plane was totally oblivious to Ben's sarcastic "You're right". :lol:

Alphanumeric this diagram from post 42 explains the high tide on the moon side of the earth.

X, Y and Z are equidistant from the earth. X and Y have fields strengths directed towards the centre of the earth.

Z does not.

Thus the field strength beneath Z all the way to the centre of the earth is less than beneath X or Y at the same distance from the centre of the earth.

Thus a high tide beneath Z and low tides beneath X and Y.

Any trouble following that I will explain further. Interesting though you have to come to pseudo science to get science.

The wobble you mention is the centre of the earth moving across its solar path as the moon orbits the earth. Both the earth and the moon move away from the sun or towards the sun in unison. Thus it is not evidence of the moon 'pulling' the earth.

PS I love how plane was totally oblivious to Ben's sarcastic "You're right". :lol:

All it says is that there is a twisted juvenile peer group within so called science, one that I have no wish to belong to.






JR, your reply does not cover your contradictions. I am questioning whether or not a small mass attracts a large mass.

Stating what the laws says does not prove the law. And you simply do not address why or how m (or M) is able to play a role in causing a force upon its self. As in F = G.M.m/ d x d.

You don't address it and I don't think you have the wherewithal to address it. Or so far you haven't shown that you are going to be able to.

F = G.M.m/ d x d

Once again how can a mass be a factor of the magnitude of a force applied to it. You never seem to have an answer. And yet you say you have 'proof' of the formula.



However, I do agree with you when you say our problem lies with Newton's third law.

I have no evidence as to whether or not it is Newton's original work. I once inquired on this forum as to whether or not it was and nobody knew.

As his first and second laws are always accepted as coming from the continent, I find it probable that the third law came down through the ages to Newton.

Newton's third law states that for every force there is an equal and opposite force.

It is a law of cause and effect. You use it so as an effect can cause a cause and vica versa.

If you want to believe that the law is other than cause and effect, I'm not going to stop you. But while you use it outside the realm of cause and effect, you are not honoring the law.

That is where the base mistake in your proof is. Unless, of course, you can prove that Newton's third law isn't a law of cause and effect.

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.

In this mess is where your problem lies.

Newton's third law says the action is the action and the reaction is the reaction.

It does not say they are interchangeable or one can be the other. That is pure invention on your part.

Action causes reaction. One before the other.

Hit a wall. That is the action.

What the wall experiences is the reaction.

When you invoke Newton's third law in a way that has action and reaction indistinguishable, you aren't invoking Newton's law.


Thus your 'proof' does not stand as you use Newton's third law in way that action and reaction are indistinguishable.

Bad luck and cheers to all.

 

[James R]

plane:

X, Y and Z are equidistant from the earth.

From your diagram, it looks like X and Z are equidistant from the Earth, and Y is further away...

Stating what the laws says does not prove the law.

You're right; it doesn't. The evidence for Newton's law of gravity is that it accurately predicts the motions of stars, planets, apples, galaxies - anything subject to gravity in fact. No law of physics exists in a vacuum. We always need to check laws against the real world. Newton's law of gravity passes every test with flying colours.

And you simply do not address why or how m (or M) is able to play a role in causing a force upon its self. As in F = G.M.m/ d x d.

On the contrary, I have already justified to you why the product of the two masses appears in the force law. Please review my previous posts.

However, I do agree with you when you say our problem lies with Newton's third law.

I have no evidence as to whether or not it is Newton's original work. I once inquired on this forum as to whether or not it was and nobody knew.

As his first and second laws are always accepted as coming from the continent, I find it probable that the third law came down through the ages to Newton.

Newton's third law was Newton's idea. It did not "come down through the ages" to Newton. But it doesn't matter, for the purposes of the current discussion.

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.

In this mess is where your problem lies.

Newton's third law says the action is the action and the reaction is the reaction.

It does not say they are interchangeable or one can be the other. That is pure invention on your part.

Action causes reaction. One before the other.

Hit a wall. That is the action.

What the wall experiences is the reaction.

When you invoke Newton's third law in a way that has action and reaction indistinguishable, you aren't invoking Newton's law.

Hit a wall with what? Your body? Let's take that as an example.

What made you decide that your body provided the "action"? Was it the fact that the wall was stationary and you were moving?

If you were standing still and a wall fell over on you, would the wall then be the "action", according to you, or is the only "action" the act of a conscious human being?

Newton's third law says that when a wall hits you, the wall exerts a force on you and you exert an equal and opposite force on the wall. Call yourself the action and the wall the reaction, or call the wall the action and you the reaction; it doesn't matter either way.

You say "action causes reaction", above. You need to explain how. Whenever the wall exerts a force on you, you simultaneously exert a force on the wall. Your force does not appear before the wall's force; it appears at the same time. So it cannot be said to "cause" the wall's force.

Understand yet?

 

[plane]

plane:



From your diagram, it looks like X and Z are equidistant from the Earth, and Y is further away...

Sorry, Alphanumeric. JR has pointed out a re pasted without due care problem. The diagram was not specifically made for your question and I replied to you without looking closely at the diagram.

X and Z are equidistant from the earth. The X points have field strengths directed towards the centre of the earth.

Z does not.

Thus the field strength beneath Z all the way to the centre of the earth is less than beneath the X points at the same distance from the centre of the earth.

Thus a high tide beneath Z and low tides beneath the X points.

Sorry Alpha. Thanks JR.

You're right; it doesn't. The evidence for Newton's law of gravity is that it accurately predicts the motions of stars, planets, apples, galaxies - anything subject to gravity in fact. No law of physics exists in a vacuum. We always need to check laws against the real world. Newton's law of gravity passes every test with flying colours.

Poetic license is still your tool. Get specific about Newton's law gravity demonstrating that a small mass attracts a large mass. Issue at hand. Refer to first post. The inverse square law or a direct proportion between mass and gravity strength is not held to question.

On the contrary, I have already justified to you why the product of the two masses appears in the force law. Please review my previous posts.

The justification?

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

It moves to newton's third law if it is and it doesn't appear that you have addressed your cause and effect issue.

Newton's third law was Newton's idea. It did not "come down through the ages" to Newton. But it doesn't matter, for the purposes of the current discussion.

Can you provide evidence that it was? Won't accuse you of unbacked up statement yet. Really like to see it if you have evidence.

Hit a wall with what? Your body? Let's take that as an example.

What made you decide that your body provided the "action"? Was it the fact that the wall was stationary and you were moving?

If you were standing still and a wall fell over on you, would the wall then be the "action", according to you, or is the only "action" the act of a conscious human being?

Newton's third law says that when a wall hits you, the wall exerts a force on you and you exert an equal and opposite force on the wall. Call yourself the action and the wall the reaction, or call the wall the action and you the reaction; it doesn't matter either way.

You say "action causes reaction", above. You need to explain how. Whenever the wall exerts a force on you, you simultaneously exert a force on the wall. Your force does not appear before the wall's force; it appears at the same time. So it cannot be said to "cause" the wall's force.

Understand yet?

Understand yet? I understand that the person hits the wall before the wall reacts to the force applied by the person. That makes the person the cause of the action and the wall the entity experiencing the reaction.

Of course if the wall fell on me it would be action and I would experience the reaction.

The action precedes the reaction.

You may think it is a deft intellectual manipulation to have the wall fall on a person, but it completely and I mean completely fails to make action and reaction indistinguishable. Would have to suspect that you knew it in your "heart" when you proposed it to. You actually seem above that sort of pathetic trickery.

Keep trying if you like but in terms of physics if it very easy to distinguish between a person hitting a wall and a wall falling on a person. (honestly if you can't see it wait till next week and I'll do you a helping diagram)

Thanks again for the diagram pick up but still yours to show that Newton's third law is not a cause and effect law.

Your proof of his law of gravity hinges on your ability to do so.

Cheers and all the best.

 

[James R]

plane:

X and Z are equidistant from the earth. The X points have field strengths directed towards the centre of the earth.

That's still wrong.

At the points X, the gravitational field vector does not point directly towards the Earth. It points off to one side, in the direction of the moon. It would only point directly towards the centre of the Earth if the moon didn't exist.

Poetic license is still your tool. Get specific about Newton's law gravity demonstrating that a small mass attracts a large mass. Issue at hand. Refer to first post. The inverse square law or a direct proportion between mass and gravity strength is not held to question.

Ok. So you don't question that gravity is an inverse-square law and that it depends on the mass of at least one of two objects. Right?

Next you need to understand is Newton's third law, and you'll understand why the gravitational force must be proportional to the product of the two masses. Finally, to understand the field at a distance from either of the masses, as at points X, Y and Z in your diagram, you need to understand the principle of superposition of forces.

Have you heard of superposition? And is Newton's third law starting to make sense to you, or do you dispute it? I'm just trying to gauge where you're at.

I have justified to you why the product of the two masses appears in the force law.

The justification?

Justification for why Newton's law of gravity says that the gravitational force is proportional to the product of the two masses.

1. You admit that the gravitational force F on mass m depends is directly proportional to the "other" mass, M, and inversely proportional to the square of the distance between the two masses.
2. By Newton's third law, if mass M produces a force F on m, then mass m must produce an equal and opposite force on mass M.
3. Hence, we conclude that the force on mass M is also directly proportional to the mass of M. (This follows from steps 1 and 2.)
4. Since the force on mass M is directly proportional to M (from step 3), and also directly proportional to mass m (from step 1, with M and m swapped), then the force is proportional to both M and m - i.e. proportional to their product.

Newton's third law was Newton's idea. It did not "come down through the ages" to Newton. But it doesn't matter, for the purposes of the current discussion.

Can you provide evidence that it was? Won't accuse you of unbacked up statement yet. Really like to see it if you have evidence.

Sure. See Newton's Principia, where Newton's third law of motion was first published. There is no prior publication containing Newton's third law.

If you believe that Newton unjustly claimed priority, you need to produce a publication from earlier than 1687 that predates Newton's publication of the third law. Otherwise, the assumption has to be that the 1687 publication by Newton was the first.

Understand yet? I understand that the person hits the wall before the wall reacts to the force applied by the person. That makes the person the cause of the action and the wall the entity experiencing the reaction.

You made a mistake. The wall does not react to the person after the person hits it. It reacts at the same time that the person hits it. I explained this fact to you earlier.

The action precedes the reaction.

No. They are simultaneous.

Until you correct this misconception of yours, you can't hope to understand Newton's third law.

Keep trying if you like but in terms of physics if it very easy to distinguish between a person hitting a wall and a wall falling on a person.

No, it isn't. There's no way to distinguish, just by analysing the forces acting on the person and/or on the wall.

I repeat my previous argument for why the apple pulls on the Earth:

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.

That's really all the "proof" that is needed.

 

[MetaKron]

This thread looks an awful lot like real science.

 

[D H]

This thread looks an awful lot like real science.

There is science here, but it is one-sided and it is not on the side of the original poster. The original post is not scientific, period. James R has been very patient and has indeed used an awful lot of real science to debunk the non-scientific concepts presented in the original post.

What is going on here? Mod wars? This thread does not being in the science section. The thread violates at least two items from the Physics&Math Alternate Theories policy:

3. Posters who are critiquing accepted physical or mathematical ideas should clearly point out what is wrong with those ideas, providing clear examples showing where the accepted theories are or may be incorrect. Preferably, such examples should be testable, backed by evidence of some kind or (in the case of mathematical criticisms) accompanied by proof.

4. Posters putting forward alternative theories should clearly explain the basic ideas of their theory, how their theory differs from conventional theories, and how their theory is likely to improve on accepted theories. Explanations should be backed by evidence. Theories should be testable and falsifiable. In short, alternative theories must be classifiable as science rather than pseudoscience.​

 

[James R]

D H:

I see this thread more as asking a question than as a critique of Newton's law of gravity. plane hasn't put forward any alternative theory either, as far as I can tell. plane wants to know how we know that an apple attracts the Earth, just as the Earth attracts an apple. I've explained it to him.

I hope that this thread may help any other person who has trouble understanding Newton's third law, in particular.

 

[plane]

That's still wrong.

At the points X, the gravitational field vector does not point directly towards the Earth. It points off to one side, in the direction of the moon. It would only point directly towards the centre of the Earth if the moon didn't exist.

No it’s not. Look at the extent of the moon’s (smaller masses) gravity on the diagram.

The egg shape is the extent of a direction of fall towards the moon. I know what you are trying to say. Your problem is you can’t substantiate a direction of fall towards the moon beyond the egg shape.

Ok. So you don't question that gravity is an inverse-square law and that it depends on the mass of at least one of two objects. Right?

Well, if you read the original post.

Newton'a law of gravity has three elements to it.

1/ The inverse square law

2/ A direct proportion between mass and gravity strength

3/ Every particle attracting every other particle.

The first two seem to pass scrutiny.

With the third can anyone point to empirical evidence of a smaller mass 'pulling' a larger mass. The tides and cavendish experiments don't do it from all the published imformation I've seen.

In the case of cavendish experiments only the small mass moves and with the high tide under the moon, all that is observed is a lesser gravitation towards the earth because of the interaction of earth and moon gravities. Which, of course isn't a gravitation towards the moon.

Next you need to understand is Newton's third law, and you'll understand why the gravitational force must be proportional to the product of the two masses.

To every action there is an equal and opposite reaction = multiply masses together. JR you are grasping at a straw. You are trying to force an opinion, not explain anything in a rational way.

Finally, to understand the field at a distance from either of the masses, as at points X, Y and Z in your diagram, you need to understand the principle of superposition of forces.

Have you heard of superposition?

Go back to the diagram. It is of field strengths. Force does not come into it.

And is Newton's third law starting to make sense to you, or do you dispute it? I'm just trying to gauge where you're at.

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.

1. You admit that the gravitational force F on mass m depends is directly proportional to the "other" mass, M, and inversely proportional to the square of the distance between the two masses.

Do not ‘admit’ this. You may recall that I have explained to you that there is no evidence that gravity is a force. Told you that the evidence is gravity either causes mass to accelerate or causes mass to become forceful (weight).

From there you are getting ahead of your self with Newton’s third law. Very much you have a mathematical approach to Newton's third law. You are not looking at as a physicists should.

Sure. See Newton's Principia, where Newton's third law of motion was first published. There is no prior publication containing Newton's third law.

If you believe that Newton unjustly claimed priority, you need to produce a publication from earlier than 1687 that predates Newton's publication of the third law. Otherwise, the assumption has to be that the 1687 publication by Newton was the first.

That’s not evidence. I mean a moment of deduction like an apple falling. It may have been his original deduction. Or given that the first two laws were not his original work, it could have come from intellectual circles of the day. Not published else where means nothing, particularly as publishing wasn’t push button as it is today.

If it’s Newton’s original work, what caused him to make the deduction?



I guess your wish to argue Newton’s law of gravity sensible is disallowing you from seeing what you are really saying. To apply Newton’s third law as you do to Newton’s law of gravity, the reaction has to be simultaneous.

So you try and bluster forth that action and reaction occur simultaneously.

Take a collision about to occur. How can a force in the opposite direction to the direction of motion of the faster moving body begin until after the collision occurs? That is just so basic.

You are trying to say the reaction occurs faster than the speed of light.

There is science here, but it is one-sided and it is not on the side of the original poster. The original post is not scientific, period. James R has been very patient and has indeed used an awful lot of real science to debunk the non-scientific concepts presented in the original post.

DH, care to elaborate on how the original post is not scientific. Just stating that something is unscientific does not make it unscientific.

Incidentally, JR is not being ‘patient’. He claims to have intellectual proof that an apple attracts the earth. And he is trying to substantiate that claim. At the moment he is hoping to being able to intellectually explain that a reaction to an action happens faster than the speed of light.

This first diagram in this post is intellectual proof that an apple does not attract the earth.

So I am just trying to get to the bottom of how and why everybody has got this wrong belief about an apple attracting the earth. Made some progress on that front. If everyone is believing a reaction occurs simultaneously with a reaction, it is fairly black and white as to where everyone is going wrong.

I hope that this thread may help any other person who has trouble understanding Newton's third law, in particular.

It won't if they start to rationalize that a reaction can occur faster than the speed of light. It will work counter to your hope if that occurs.

 

[D H]

No it’s not. Look at the extent of the moon’s (smaller masses) gravity on the diagram.

Stop with the silly diagram. Physical theories are mathematical explanations of how we observe the universe is, not how we want it to be.

Observation piled upon observation have shown that gravity makes masses attract other masses. That the Earth attracts the Moon and that the Moon attracts the Earth are observable facts.

DH, care to elaborate on how the original post is not scientific. Just stating that something is unscientific does not make it unscientific.

There is nothing scientific in that post, or in any of your posts. You do not offer any alternative theories. You do not propose new experiments that would falsify extant theories of gravity while validating yours. You do not point out any experiments that falsify the concept that all particles are attracted to all other particles gravitationally. All you do is claim a dislike for this concept. Science is about determining how the world is. How the world "should" be is the domain of religion, politics, and philosophy.

That objects attract one another is an observable scientific fact. We don't know exactly why this is so, or even the exact nature of the attraction. Newton proposed one scheme based on observations (not wishes). Einstein proposed another scheme based on more refined observations (not refined wishes). Except in the case of large, concentrated masses or very rapidly moving objects, general relativity simplifies to Newtonian gravity.

 

[flameofanor5]

I really should avoid this part of sciforums because I have no clue what's being discussed. o-o

 

[Vkothii]

Take a collision about to occur.

OK, there are two cars headed straight towards a point (of collision) from opposite directions - let's make it from due north and due south towards this point.

How can a force in the opposite direction to the direction of motion of the faster moving body begin until after the collision occurs?

It can't. There is no "force" in either direction after the collision. But during the collision there is.

"That is just so basic."

Try another example - an apple hanging on a tree. The apple is nice & ripe looking - maybe it will "fall off" the tree soon? Try to think of simultaneous actions and forces, instead of "before" and "after".
Examine (if possible) the "forces" acting on the apple: one (gravity) is "pulling" the apple downwards towards the ground; the other - opposing "force" is keeping the apple stuck to the tree - this is due to the cells (made of strong protein materials like lignin and also cellulose polymers).

There's a layer of cells at the "tree" end of the stem (the thing connecting the apple and responsible for the opposing force), that changes slowly - the abscission layer. Cells in the abscission layer die off slowly and release the hold (continuous connection) that the apple + stem has. Eventually, the layer becomes discontinuous, or sufficiently disconnected so that gravity "forces" the apple to disconnect altogether from the tree - it falls to the ground.
The "cause" is gravity, and the gradual changes (death and discontinuity) in the layer of cells in the stem. Two things -two opposite "forces".

Gravity is apparent as a force when two (or more) masses are present in "space".
The forces are present (simultaneously) from both (or each) mass, and exert a "pull" or attraction on the other (or each other) mass.
Gravity is not apparent from just one mass - but there is no way to "measure" gravity without using another mass - right?

 

[James R]

plane:

At the points X, the gravitational field vector does not point directly towards the Earth. It points off to one side, in the direction of the moon. It would only point directly towards the centre of the Earth if the moon didn't exist.

No it’s not. Look at the extent of the moon’s (smaller masses) gravity on the diagram.

The egg shape is the extent of a direction of fall towards the moon. I know what you are trying to say. Your problem is you can’t substantiate a direction of fall towards the moon beyond the egg shape.

You yourself have agreed that gravity is an inverse-square law. Therefore, the Moon's gravity extends to infinity, and not just within your "egg shape".

Your diagram is clearly incorrect. The moon's gravity does not suddenly stop at the boundary of your egg. Nor does the Earth's gravity stop at point Z on your diagram. If it did, the moon would not be in orbit around the Earth, because it would be out of Earth's "egg".

Moreover, it is an experimentally observable fact that a body placed at point X in your diagram will NOT accelerate straight towards the centre of the Earth. The reason is that the moon's gravity also pulls on it, just as the Earth's does.

Go back to the diagram. It is of field strengths. Force does not come into it.

Do you know what force and field are? You sound like you have no idea.

You may recall that I have explained to you that there is no evidence that gravity is a force. Told you that the evidence is gravity either causes mass to accelerate or causes mass to become forceful (weight).

Please review my previous posts where I walked you through the implications of Newton's second law, relating force and acceleration.

If it’s Newton’s original work, what caused him to make the deduction?

Try reading the Principia. You might find what you're looking for in there.

So you try and bluster forth that action and reaction occur simultaneously.

Take a collision about to occur. How can a force in the opposite direction to the direction of motion of the faster moving body begin until after the collision occurs? That is just so basic.

It is indeed basic. There's no point in my repeating myself, so I'm not going to. You need to make an effort to learn this stuff yourself. And for that, you need to want to learn.

You are trying to say the reaction occurs faster than the speed of light.

Force does not have a "speed". Your idea makes no sense at all. Moreover, this is a straw man, since I made no such statement.

Incidentally, JR is not being ‘patient’. He claims to have intellectual proof that an apple attracts the earth.

I have a presented clear, step-by-step justification, twice now. Both times, you have ignored it.

I'm beginning to regard you as a troll. I can't see that further discourse with you is likely to be fruitful.

So I am just trying to get to the bottom of how and why everybody has got this wrong belief about an apple attracting the earth.

Has it occurred to you that, just possibly, it may be that everybody else in the world is right and you are wrong?

 

[BenTheMan]

plane---

Did you ever explain why the wobble in a star is NOT caused by the gravitational influence of an orbiting body?

 

[plane]

The point of raising the issue is, according to Newton’s third law, directly opposite the above arrow the weight of the earth should be a construct of 9.799 m/s/s. Not 9.8 m/s/s. It is being suggested to the learned that the explanation of the high tide on the opposite side of the earth is an equal and opposite reaction to the one induced on the other side by the moon.

This could be important to science.

I have misplaced my copy of Principia but if you read Newton’s introduction to universal gravitation where he declares that we must allow that all bodies whatsoever are endowed with a principal of mutual gravitation, the only small mass he cites as ‘attracting’ a larger mass is the moon to the earth through the tides.

If he has mathematically mistaken a lesser gravitation towards the earth for a gravitation towards the moon, you can see there is a chink in the ogic about a smaller mass attracting a larger mass.

In Cavendish experiments, the large mass is not observed to move.

It can't. There is no "force" in either direction after the collision. But during the collision there is.

During does not equal simultaneous. During equals a series of cause and effect actions and reactions. JR has the problem of making action and reaction simultaneous and not cause and effect. That does not help him.

Force does not have a "speed".

Force travels through matter. Apply a force to one side of anything. It is not instantaneously felt on the other side. E.G. (vivid) Pushing passengers on a train in Japan.