[Smokinjoe9]

TeleMad said:

If the occupants were being pulled by a DIFFERENT STRENGTH of the Earth' gravity then they would. But the spacestation and everything in it experiences the same downward graviational pull, because they are all the same distance from the Earth's center of mass, so they are all effected to the same degree. They all fall towards the Earth is the same arc, so the occupants don't get pushed to one side or the other.

Got it, more studying....

[Smokinjoe9]

TeleMad said:

Sorry, I don't understand what you are getting at in this part: "There was no force greater than the mass/weight of the at rest ball exerted by it..."

The at-rest ball is hit by the moving ball. The moving ball transfers some (or all) of its kinetic energy to the other ball, causing the other ball to move with a particular accleration, according to Newton's second law. Because the formerly at-rest ball 'pushes back' against the moving ball, in accordance with Newton's third law, the moving ball's velocity changes noticeably.

The ball at rest cannot create force, it can however have mass/weight, therefore the ball at rest cannot "push back"...The moving ball's velocity changes due to contact with another mass/ball, not by the force of the other ball??? I understand once the moving ball comes in contact with the at rest ball, then the at rest ball will cause resistance and accelerate because of mass. how does it push back, it has no force and only resists force?

[TeleMad]

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TeleMad: But note that scientists can show that 2 objects side by side hear at the surface do attract each other gravitationally. I believe it was Cavendish who did this first: they took solid metal spheres and supsended them from wires: they could measure the change in the angle of the devices caused by the "sideways" gravitational attraction between the two lead spheres.

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Smokingjoe9: Interesting...there could be many reasons for the angle, just a couple, relaxation in the wire, tempurature,I am not doubting the test, I will have to see the results, I am just thinking....Sounds like a good test to make...

The results were as predicted by Newton's equation F = G(mM) / d^2 and were attractive. The only force known that would cause this type of relationship - for macroscopic, non-charged objects - is gravity.

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"The experiment was carefully repeated with different masses at various separations. In addition to providing a value for G, the results showed that the force is attractive, proportional to the produce mM [that is, my M1 * m2], and inversely proportional to the square of the distance r." (College Physics: Fifth Edition, Serway & Faughn, Harcourt College Publishers, 1999, p195-196)

[Smokinjoe9]

TeleMad said:

The results were as predicted by Newton's equation F = G(mM) / d^2 and were attractive. The only force known that would cause this type of relationship - for macroscopic, non-charged objects - is gravity.

Got it, but sadly if gravity is the cause we need to know what gravity is????
I like it, I am still not throughly convinced, the math seems right, but is based on some theoretical data(gravity etc..) i am starting to hate science

[TeleMad]

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TeleMad: If the occupants were being pulled by a DIFFERENT STRENGTH of the Earth' gravity then they would. But the spacestation and everything in it experiences the same downward graviational pull, because they are all the same distance from the Earth's center of mass, so they are all effected to the same degree. They all fall towards the Earth is the same arc, so the occupants don't get pushed to one side or the other.

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Smokinjoe9: Got it, more studying....

Let's look at Newtons equation for universal gravitation.

F = G(mM / r^2)

F is the force of attraction between two objects.
G is the universal gravitation constant
m and M are the masses of the two objects
r is the radius: that is, the distance separating the two objects' centers of mass

We simplify this a bit by getting rid of G: we just have to change the equation to being only a proportionality. I'll use the ~ to indicate "is proportional to"

F ~ mM / r^2

What this says is that the force of attraction between two objects is (1) directly proportional to the product of their masses, and (2) inversely proportional to the square of the distance separating the two objects' centers of mass.

If we get less technical we can simplify that too.

F ~ mM / r^2

What this says is that the force of attraction between two objects is determined by two factors: their masses and the distance between them: (1) the more massive the objects the stronger the force, and (2) the greater the distance between them the weaker the force.

So for objects at the same distance from the center of the Earth, r and r^2 is the same. Since this is the case for the spaceship in orbit, we can simlify this even more by eliminated r^2.

F ~ mM

What this says is that for any object that is a given distance away from the center of the Earth, the force of attraction between the object and the Earth is proportional to the mass of the object.

But since the Earth is always being used here, we can eliminate it too.



Here's the final, fully simplified 'equation':

F ~ m

What this says is that for any object that is a certain distance away from the center of the Earth, the force of attraction it experiences is proportional to its mass


That makes it sound like an astronaut in the orbiting spaceship would experience a greater force of attraction towards the Earth's center of mass than would a basketball in the spaceship. AND IT WOULD!

But remember Newton's second law: a = f / m

If you have two objects A and B (astronaut and ball) where the mass of A is 100 times that of B, then A will experience 100 times stronger force pulling him towards the Earth. HOWEVER, having 100 time the mass, it will also take 100 times the force to produce the same acceleration!

So mass cancels out. Thus, all objects in the orbiting spaceship experience the same acceleration. They arell pulled out of straight line motion to the very same degree. Consequently, they all follow the same arched trajectory across the sky, and an astronaut it not flung up against a wall.

[Smokinjoe9]

I hope this is not to boring, and I appreciate all the input. I will ask crazy questions, and doubt many answers, but, that seems to help me learn, well and waste your time Thanks to everyone.......

[TeleMad]

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TeleMad: The results were as predicted by Newton's equation F = G(mM) / d^2 and were attractive. The only force known that would cause this type of relationship - for macroscopic, non-charged objects - is gravity.

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Smokingjoe9: Got it, but sadly if gravity is the cause we need to know what gravity is????

What Newton did was mathematically DESCRIBE gravity: he didn't explain it.

It was Einstein who EXPLAINED gravity. Gravity is the warping of spacetime by mass, and the resulting acceleration objects in motion experience due the warping of spacetime.

An analogy often used involves two solid metal spheres and a stretched rubber sheet. Role one sphere across the stretched rubber sheet: it moves in straight line motion at constant speed (as far as we are concerned here: friction actually slows it down, but that's irrelevant). Now place one of the solid metal spheres in the center of the rubber sheet such that sheet is deformed: the sphere causes the sheet to invaginate around it. Now roll the other sphere across the sheet: this time, the moving ball will curve in towards the other sphere: it's path will be deflected - accelerated - by the warping of the rubber sheet, in a direction towards that other sphere.

[Smokinjoe9]

TeleMad said:

Let's look at Newtons equation for universal gravitation.

Here's the final, fully simplified 'equation':

F ~ m

Got it....It's eloquent, and I hope it is correct...

[Smokinjoe9]

TeleMad said:

What Newton did was mathematically DESCRIBE gravity: he didn't explain it.

It was Einstein who EXPLAINED gravity. Gravity is the warping of spacetime by mass, and the resulting acceleration objects in motion experience due the warping of spacetime.

This I knew...

TeleMad said:

An analogy often used involves two solid metal spheres and a stretched rubber sheet. Role one sphere across the stretched rubber sheet: it moves in straight line motion at constant speed (as far as we are concerned here: friction actually slows it down, but that's irrelevant). Now place one of the solid metal spheres in the center of the rubber sheet such that sheet is deformed: the sphere causes the sheet to invaginate around it. Now roll the other sphere across the sheet: this time, the moving ball will curve in towards the other sphere: it's path will be deflected - accelerated - by the warping of the rubber sheet, in a direction towards that other sphere.

This I hate, it even sounds rediculous, I mean, I've read the grid version, I just don't like it..WAIT, I didn't say it was wrong, but I have that feeling and if so, well...They seem to think the dark matter theory may not lead way to general relativity, but that's another story for me...

[TeleMad]

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Smokinjoe9: The ball at rest cannot create force, it can however have mass/weight, therefore the ball at rest cannot "push back"...The moving ball's velocity changes due to contact with another mass/ball, not by the force of the other ball??? I understand once the moving ball comes in contact with the at rest ball, then the at rest ball will cause resistance and accelerate because of mass. how does it push back, it has no force and only resists force?

First, what is a force? In simplest terms it is a push or pull. Does the at-rest ball exert a push against the moving ball? Yes. We can see that. For example, if it is a glancing blow then the originally moving ball will be sent off in a new direction. The at-rest ball pushed the moving ball off into that other direction: if it didn't the moving ball would have continued to move in a straight line.

Another way to consider this. Newton's second law states that a = F / m. For the moving ball, the acceleration changes: that is, it's speed and/or direction changes after contacting the originally at-rest ball. If the moving ball accelerated, then a force MUST have acted on it; for if F = 0, then A = 0, yet we know that A is NOT equal to 0. What could have produced that force? The other ball.

We could also go lower and consider force to be an interaction between objects, such as the electric force that causes like charge to repel and opposite charges to attract, or the gravitational force that attracts masses to one another, or the strong force that attracts quarks to each to form protons and other subatomic particles, and the weak force that causes radioactive decay of some nuclei. Does the billiard ball example involve any of these forces/interactions? Yes, the electic force. At the smaller level, what happes is that the atoms one ball approach the atoms of the other ball. The electron shells of the atoms of the two balls interact with one another, in a repulsive manner. So ultimately it is the electrical repulsion of like charges at the atomic scale that is responsible for the force the at-rest ball exerts on the moving ball.


PS: I assume that's a low-enough level of explanation for you. We could one level deeper and look at how the electric force itself works, which involves the exchanging of virutal photons between charges: but that seems TOO deep for this discussion.

[Mac]

Smokinjoe9 said:

Ok, I'm getting there, I first have to get past..An object has gravity because it has mass????? I'm working on it, I have not done the experiments myself so, I have to assume this is correct...hypothetically, 2 rocks places side by side in space do not attract they just sit there, correct?
I mean if I set them side by side(sitting still) in space they wil no come together, right?

Yes, two rocks in space, even across the universe from each other ( according to current theory) attract each other and with no other forces involved would one day come together.

However, the discovery of the accelerating expansion of the universe creates some question about that. It would appear that at some distance gravity may become repulsive rather than attractive.

Mathematically at least Dark Energy may be the cause of both gravity and the expansion.

http://www.unikef-gravity.com/

[Smokinjoe9]

TeleMad said:

First, what is a force? In simplest terms it is a push or pull. Does the at-rest ball exert a push against the moving ball? Yes. We can see that. For example, if it is a glancing blow then the originally moving ball will be sent off in a new direction. The at-rest ball pushed the moving ball off into that other direction: if it didn't the moving ball would have continued to move in a straight line.

Another way to consider this. Newton's second law states that a = F / m. For the moving ball, the acceleration changes: that is, it's speed and/or direction changes after contacting the originally at-rest ball. If the moving ball accelerated, then a force MUST have acted on it; for if F = 0, then A = 0, yet we know that A is NOT equal to 0. What could have produced that force? The other ball.

We could also go lower and consider force to be an interaction between objects, such as the electric force that causes like charge to repel and opposite charges to attract, or the gravitational force that attracts masses to one another, or the strong force that attracts quarks to each to form protons and other subatomic particles, and the weak force that causes radioactive decay of some nuclei. Does the billiard ball example involve any of these forces/interactions? Yes, the electic force. At the smaller level, what happes is that the atoms one ball approach the atoms of the other ball. The electron shells of the atoms of the two balls interact with one another, in a repulsive manner. So ultimately it is the electrical repulsion of like charges at the atomic scale that is responsible for the force the at-rest ball exerts on the moving ball.


PS: I assume that's a low-enough level of explanation for you. We could one level deeper and look at how the electric force itself works, which involves the exchanging of virutal photons between charges: but that seems TOO deep for this discussion.

Is the opposite force created because of the impact, this I can grasp?
Energy is transformed, energy is absorbed, energy is converted, energy is exchanged, energy is created, but only after the contact of the two, right.

[TeleMad]

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Smokinjoe9: Is the opposite force created because of the impact, this I can grasp?

Basically, yes. But it seemed you wanted a deeper explanation of how that occurred. Where EXACTLY did the force come from.

Thought of an analogy. Take two straight bar magnets; place one at rest on a smooth surface with the south pole facing you, and hold the other one ridigly in your hand, with the south pole facing the other magnetic. Slowly move the magnet in your hand towards the at-rest magnet. The at-rest magnet will begin to move away, being repulsed by the like magnetic field its south pole is experiencing. Now do it again, but this time hold the bar magnet in your hand very, very loosely. As you bring it close to the at-rest magnet, you will feel the magnet in your hand being pushed backwards, away from the other magnet because of the repulsion between like magnetic fields. We see that the moving bar magnet exerts a force on the at-rest bar magnet, and the at-rest magnet exerts a force on the moving bar magnet, even though the two never actually come into direct physical contact.

The same general thing happens to billiard balls at the atomic scale, but there it is the like electric charges of the negatively charged electron clouds approaching one another that exert a force from one ball to the other, and vice versa.

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Smokinjoe9: Energy is transformed, energy is absorbed, energy is converted, energy is exchanged, energy is created, but only after the contact of the two, right.

Well, the main energy process is that some (or most) of the kinetic energy of the moving ball is transferred to the at-rest ball.

There is transformation and conversion of energy. For example, the "clack" you hear when the balls collide is some of the kinetic energy of the moving ball being converted into sound energy: energy being carried away from the collision as wave disturbances in air. Also, some of the kinetic energy is converted into heat: you might not be able to feel the difference, but the two balls would be very slightly warmer after the collision than before.

Energy isn't created in the process.

[Smokinjoe9]

TeleMad said:

Basically, yes. But it seemed you wanted a deeper explanation of how that occurred. Where EXACTLY did the force come from.

Thought of an analogy. Take two straight bar magnets; place one at rest on a smooth surface with the south pole facing you, and hold the other one ridigly in your hand, with the south pole facing the other magnetic. Slowly move the magnet in your hand towards the at-rest magnet. The at-rest magnet will begin to move away, being repulsed by the like magnetic field its south pole is experiencing. Now do it again, but this time hold the bar magnet in your hand very, very loosely. As you bring it close to the at-rest magnet, you will feel the magnet in your hand being pushed backwards, away from the other magnet because of the repulsion between like magnetic fields. We see that the moving bar magnet exerts a force on the at-rest bar magnet, and the at-rest magnet exerts a force on the moving bar magnet, even though the two never actually come into direct physical contact.

The same general thing happens to billiard balls at the atomic scale, but there it is the like electric charges of the negatively charged electron clouds approaching one another that exert a force from one ball to the other, and vice versa.



Well, the main energy process is that some (or most) of the kinetic energy of the moving ball is transferred to the at-rest ball.

There is transformation and conversion of energy. For example, the "clack" you hear when the balls collide is some of the kinetic energy of the moving ball being converted into sound energy: energy being carried away from the collision as wave disturbances in air. Also, some of the kinetic energy is converted into heat: you might not be able to feel the difference, but the two balls would be very slightly warmer after the collision than before.

Energy isn't created in the process.

This I understand, thank you...So, where does the attraction of gravity come in, some of the kinetic energy must be used up by the force of gravity due to the balls having mass, right? Can this be measured? I mean the closer the balls get together the more gravity(due to the mass of each) wil pull the objects together, right.

[paultrr]

Smokinjoe9 said:

This I understand, thank you...So, where does the attraction of gravity come in, some of the kinetic energy must be used up by the force of gravity due to the balls having mass, right? Can this be measured? I mean the closer the balls get together the more gravity(due to the mass of each) wil pull the objects together, right.

By the book all energy yields a local gravity field. This would even apply to particles. But measuring such for small objects is beyond our ability. Gravity as a force is 1000 times weaker than EM itself. For small objects like say a small rock from someone's backyard or a baseball the field is almost non-existant.

Dark matter is different from dark energy. Dark matter has a positive energy. It just does not admit any measurable light or energy that we can directly view. Dark energy, known by several different names based upon different theories to account for it produces the opposite effect of normal matter. It yields an effect that works opposite of gravity and causes spacetime to expand even more. Some theories liken it to exotic energy, some vacuum energy, etc. As far as effect goes its like anti-gravity. Dark matter does not produce it. Dark matter actually adds to all the matter/energy generated gravity in the universe. If there is any sort of matter attached to this dark energy it would be something way beyond either regular matter or dark matter.

Energy is never created or distroyed. It changes form only. Even the BB by the theory is not creation of energy from nothing, Its creation of energy from vacuum energy which by the book was far higher before the end of inflation than now. Here vacuum energy altered form into the matter/energy we see around us in the universe. The amount of energy remains the same. But its distribution is different now.