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As an addendum to my last post I might mention that there has been a lot of philosophical discussion about why the universe seems to be mathematical. People who think deeply about this don't see any reason why the universe should be able to be described in mathematical terms. For example one of the primary descriptions in physics is F=MA. That is the force applied to an object is equal to the mass of the object multiplied by the acceleration of the object. This has been shown to be true, but philosophers don't see any good reason why it should be true.

So when we develop theories about the universe they all wind up being mathematical in nature. The best that most scientists can say to this is that that is the way it is. Philosophers of course want to know why things work, not just that they do.

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Thanks for that post, bill. Well put.

As many forum readers may be aware, Mario Livio's book: "Is God a mathematician?" considers this question.

http://plus.maths.org/content/god-mathematician
http://www.mariolivio.com/




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Originally Posted By: Bill

Well, in that case you need to provide a good physical definition of the Newton's laws without using any math

I think you have slightly misread my post. I meant that the 'physical world' is to be defined physically, not 'Newtons laws'. For example, you have to define matter, energy and force physically. I have my own definitions for these. I think this forum does not impose much restrictions to such alternate views (unlike some other forums). I will give the definitions in the next post.

F=ma is a mathematical relation, not a physical law (in my opinion). However, at present this is used as a definition for force, and so it is held that force imparts energy. But, being a mathematical relation, when we apply it to physical systems, we have to mention from which source the energy comes. If enough energy is not supplied, the acceleration will not be proportional to the force. That is the difference that I propose.

What you have said about philosophers is correct. However, there is strange relationship between mathematics and philosophy. I think both can deal with non-real situations. That is, mathematicians tend to be philosophers.

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Originally Posted By: finiter

I think you have slightly misread my post. I meant that the 'physical world' is to be defined physically, not 'Newtons laws'. For example, you have to define matter, energy and force physically. I have my own definitions for these. I think this forum does not impose much restrictions to such alternate views (unlike some other forums). I will give the definitions in the next post.

That is what I was trying to say. You must somehow relate your definition of the physical world to how it works. That means you have to supply Finiter laws that are your equivalent of Newtons laws.

Originally Posted By: finiter
F=ma is a mathematical relation, not a physical law (in my opinion). However, at present this is used as a definition for force, and so it is held that force imparts energy. But, being a mathematical relation, when we apply it to physical systems, we have to mention from which source the energy comes. If enough energy is not supplied, the acceleration will not be proportional to the force. That is the difference that I propose

Unfortunately that is just not so. The acceleration will always be proportional to the force. The energy difference between the state of an object before a force is applied and the state after the force has been applied will be the integral of the mass times the acceleration. What that amounts to is the energy gained by the object, which is the mass of the object multiplied by the velocity gained by the object, e = m(v2-v1)^2. There is no way that f = ma will be violated.

Bill Gill


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Originally Posted By: Finiter
If enough energy is not supplied, the acceleration will not be proportional to the force.


Finiter, while I agree entirely with Bill Gill's last comment, I would be fascinated to know the circumstances in which you believe f = ma can be violated; outside the quantum world, that is.


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Force can be defined physically as follows: Force is something that can cause changes in a body. To know how much force you apply, you can use the mathematical relation, F=ma. The relation does not say what changes happen to the body (whether its speed changes, whether there is an energy transfer, etc.). It tells only that the force applied is enough to create a certain acceleration.

For example, in the case of a body orbiting in a gravitational field, the force does not change the speed, if the orbit is circular. In the case of an elliptical orbit, the speed varies and the energy required for the change in speed is adjusted from the internal energy of the body. In both the cases the body does not get enough energy (from outside) for an acceleration. In the case of mechanical force, the body is always in contact with the surroundings, and the energy transfer from the surroundings provide the required energy. So the energy transferred is equivalent to create the required acceleration.

The above explanation is based on the physical definition of force. I am not sure whether it will be possible to explain each and every case or whether there will be any dead end. Anyway, it is logical up to what is given above.

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Originally Posted By: finiter
The above explanation is based on the physical definition of force.

But you haven't given us a physical definition of force. What you say doesn't mean anything without a definition of terms.

And backing up a bit you say that in an orbiting body the force doesn't change the speed. But it does change the velocity. Speed is a scalar quantity. That is it has only magnitude. Velocity is a vector quantity, it includes a magnitude and a direction. An orbiting body is always changing the direction in which it is moving. The energy of a moving body is (1/2)*m*v^2. Therefore the acceleration is still F = MA. I know you don't like math in your system, but until you develop a way to do it some other way that is what we are stuck with.

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My definition has already been given. 'Force is something that can create changes in a body'.

Not that I don't like mathematics in the system. Mathematics is the tool, and it should remain as such, 'a toll to quantify mass, energy, force etc'. And there is no other tool other than mathematics. But, mathematical definitions are improper. The mathematical definition of force gives the wrong (in my opinion) notion that force imparts energy. What I argue is force cannot impart energy.

The speed of the orbiting body does not increase; that means its energy does not increase. Technically, based on the mathematical definition of force, you can say that it is accelerated towards the centre of the circular orbit. Actually it is the force that is acting towards the centre. When we ask,"How much force?". Then the answer comes, " force enough to create certain acceleration".

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Originally Posted By: finiter
My definition has already been given. 'Force is something that can create changes in a body'.

The mathematical definition of force gives the wrong (in my opinion) notion that force imparts energy. What I argue is force cannot impart energy.


Rather than saying force imparts energy a better way to say it is to say that force transfers energy. The total energy in a system is constant. A force is capable of transferring energy from one part of the system to another.

You say that "The speed of the orbiting body does not increase". It may or may not depending on the orbit. But the velocity of the orbiting body does. If you use the mathematical tools to calculate the change you will find out that it all comes out even.

You say that you don't like mathematical laws of the universe. Just think about it a little and you may realize that the mathematics is just a tool to describe the laws. When we say f = ma then we are saying that the mathematical formula describes the physical fact that a push (or pull) causes a mass to change its velocity in a specific way. You are objecting to the math and saying that the math is the law. The math is simply a shorthand way to describe the law.

Bill Gill


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Originally Posted By: Bill

Rather than saying force imparts energy a better way to say it is to say that force transfers energy.... from one part of the system to another.

I agree with what you say, but some clarification regarding the nature of the system is required. Earth is system on its own. Moon is a system on its own. However, the earth and the moon together form a system.

On the earth, transfer of energy is possible by collisions between atoms. But between earth and moon no such collision is possible. So when gravity acts, no energy transfer can take place between the two. But, it is held that gravity imparts energy to the moon. The orbit of moon is slightly elliptical, and the variation in speed is taken as a consequence of energy being imparted. That is, during a revolution, the total energy of the moon remains varying .

What I argue is that just because force exists between earth and the moon, there is no transfer of energy between the two. The slight variation in the speed of the moon is due to transfer of energy within the moon. That is, even though the speed varies, the energy of the moon always remains the same. I think you have understood my point.

The above difference, I think, is due to the mathematical definition that F= ma, which implies that force acting on a distance imparts energy.

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There is a massive falacy on your thinking finiter.

You can't EVER I do mean EVER have a sigular force do you understand why that is?

If you think you can give me an example.

In the earth-moon system there are two balancing forces do you know what they are?

Trust me there is energy exchange involved and alot of it.

Last edited by Orac; 09/04/11 08:26 AM.

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About a year ago in the thread This is a different take on what gravity is we knocked this about for around three pages without reaching any real conclusion.

Could we have better luck this time?


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Originally Posted By: Orac
Trust me there is energy exchange involved and alot of it.


Would it be true to say that when energy exchange occurs in a system, energy is lost from that system; otherwise perpetual motion would be a possibility?


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Originally Posted By: Finiter
What I argue is that just because force exists between earth and the moon, there is no transfer of energy between the two.


I guess this is the same question that Orac is asking in different words, but how do you perceive a force existing between two bodeis without an exchange of energy?


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It is not just a possibility it is happening and always does, there is no perpetual energy even in space
(http://en.wikipedia.org/wiki/Tidal_acceleration)

The Moon is generating vast amounts of energy on the Earth's surface as it generates the tidal bulge. Those tides dissipate about 3.3 to 4 tW of energy (3.3 to 4 10E12 watts). The effect is the moon is moving slightly away each year as Earth transfers energy to the moon.

There are two alternate views on what will happen in 15 Billion years time with the moon at 1.6 times its current distance and a lunar period of 55 days.

i). The moon will stabilize and no longer cause tides. This will happen because the earth will at that point have the one side of earth always facing the moon as the one side of the moon faces earth now. So the tidal bulge will exists but be permanently still. So now the energy dissiapation will drop to a much lower level.

ii). At this locking point the moon is periously close to becoming retrograde because the earth is at present only 55% of the attractive force of the sun on the moon. At that distance it is very close to 50-50% the amount of weight the sun sheds between now and then is at best a guess at the moment.


The earth orbital change is harder to work because the sun is shedding mass as it burns (http://en.wikipedia.org/wiki/Earth's_orbit)

Anyone who tells you anyting with certainty about Earth's orbit is lying the n-body proof has even made it into wikipedia

Quote:

In 1989, Jacques Laskar's work showed that the Earth's orbit (as well as the orbits of all the inner planets) is chaotic and that an error as small as 15 metres in measuring the initial position of the Earth today would make it impossible to predict where the Earth would be in its orbit in just over 100 million years' time. Modeling the solar system is subject to the n-body problem.


There are simply too many bodies in play around the sun to say anything with certainty they can be adding or removing energy just as the Earth-moon system is.

Last edited by Orac; 09/04/11 02:10 PM.

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Going back just a little Finiter wants to have the laws of the universe recast in physical terms rather than mathematical terms. After my reply to him yesterday regarding f=ma I realized that most of the laws are indeed cast in physical terms. It is especially easy to see in the case of Newton's laws.

I. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

II. The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma. Acceleration and force are vectors (as indicated by their symbols being displayed in slant bold font); in this law the direction of the force vector is the same as the direction of the acceleration vector.

III. For every action there is an equal and opposite reaction.

Notice that the second law is the only one that actually includes a mathematical formula. As I stated in my previous post that can be stated: When we say F is F=ma then we are saying that the mathematical formula describes the physical fact that a push (or pull) causes a mass to change its velocity in a specific way.

So I don't see where Finiter's problem is. Except that he apparently doesn't understand just how energy works.

Bill Gill
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Originally Posted By: Orac
It is not just a possibility it is happening and always does, there is no perpetual energy even in space


You seem to be saying that perpetual motion is happening all the time. The link you cited states that energy is constantly being lost from the Earth/moon system; so this is not an example of perpetual motion - it will come to an end.

Perhaps you mean that once set in motion, a body will remain in motion until something acts upon it to stop it? I can see that by this definition, most of the motion in the Universe could be considered as perpetual motion.

Could this mean that it is not perpetual motion that is impossible to achieve; it is only the extraction of work from perpetual motion that is forbidden?


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I think what Orac was saying wasn't what you read. I think he meant there is no perpetual motion even in space.

Now I will give my take on perpetual motion in space.

Imagine a universe with just 2 perfect masses in it. That is they are point source masses. Assume they are in a circular orbit around their common center of mass. I believe this is one stable solution to the 2 body problem. Under these conditions I believe you would have a system in perpetual motion. They would circle each other for eternity.

Now let's look at the real universe. If we start with 2 bodies circling each other we will have something that at first looks like the system in the first example. But in the real universe there are a lot of other factors involved. For one thing the 2 bodies aren't perfect point sources. They are extended bodies and they aren't perfectly inelastic. So there will be tidal effects. The tidal effects will remove energy from the 2 masses and dissipate it as heat. Therefore the orbits will change. Also there are other bodies in the universe and gravitational effects from the other bodies will cause the orbits to be perturbed. So due to energy exchanges with the other bodies the orbits will once again be perturbed. So in the real universe there is no real perpetual motion.

Face it, the people who have tried over and over to build perpetual motion machines have come up against the same problem. Losses due to friction cause the machine to slow and eventually stop.

I suppose that the universe as a whole might represent a sort of perpetual motion, but that depends on the overall evolution of the universe. That is far beyond anything I am prepared to speculate on. I do figure that that really gets into the realm of speculation.

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Originally Posted By: Bill
I think what Orac was saying wasn't what you read. I think he meant there is no perpetual motion even in space.


Correct Bill that darn english thing again :-)


Originally Posted By: Bill

Now I will give my take on perpetual motion in space.

Imagine a universe with just 2 perfect masses in it. That is they are point source masses. Assume they are in a circular orbit around their common center of mass. I believe this is one stable solution to the 2 body problem. Under these conditions I believe you would have a system in perpetual motion. They would circle each other for eternity.


Nope not even if you make the two bodies perfect you would have to extend your universe to be a perfect vacuum as well as your two planets would bump into the few molecules floating around imparting them with energy and slowing down be it ever so infintesimal.


Originally Posted By: Bill

I suppose that the universe as a whole might represent a sort of perpetual motion, but that depends on the overall evolution of the universe. That is far beyond anything I am prepared to speculate on. I do figure that that really gets into the realm of speculation.
Bill Gill


Thats the same view as all the smart money in physicist circles :-)


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Originally Posted By: Orac


Originally Posted By: Bill

Now I will give my take on perpetual motion in space.

Imagine a universe with just 2 perfect masses in it. That is they are point source masses. Assume they are in a circular orbit around their common center of mass. I believe this is one stable solution to the 2 body problem. Under these conditions I believe you would have a system in perpetual motion. They would circle each other for eternity.


Nope not even if you make the two bodies perfect you would have to extend your universe to be a perfect vacuum as well as your two planets would bump into the few molecules floating around imparting them with energy and slowing down be it ever so infintesimal.



That was part of my set up. I said that there were just 2 perfect masses. That excludes all other matter. So, no dust, no nothing, they should orbit forever.

Of course this is in a Newtonian universe. I'm not sure what QM would do to them.

Bill Gill


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