Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: !mater on 13/07/2011 19:46:43
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I mean, i push a Atom, how does it remember i pushed it, storing kinetic energy, to deliver on impact? I know its kind of a too simple question, but why not ask it anyway... better to die as the reason for some good laughs, then to vanish as a silent fool!
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It doesn't need to "remember" that you pushed it; conservation of energy is what says that it must move if pushed. Here's another way of thinking of it: if an atom is not being accelerated from behind, not being slowed down from the front, and not being pushed from either side, then it's only logical that it will maintain its current momentum (whether that moment is zero or very large). If the atom "forgot" that you pushed it and slowed down, that would be equivalent to a force acting on it to slow it down. If no such forces are present, then it will not slow down.
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It doesn't need to "remember" that you pushed it; conservation of energy is what says that it must move if pushed. Here's another way of thinking of it: if an atom is not being accelerated from behind, not being slowed down from the front, and not being pushed from either side, then it's only logical that it will maintain its current momentum (whether that moment is zero or very large). If the atom "forgot" that you pushed it and slowed down, that would be equivalent to a force acting on it to slow it down. If no such forces are present, then it will not slow down.
Well, yes, but that doesn't really explain why it doesn't stop moving as soon as you stop pushing it.
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try a sponge
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When you push an object it resists by pushing back (inertia) and it accelerates (this if you like creates the "memory" of its pushing). It will continue to accelerate as long as you continue to push it. When you stop pushing it will continue to be in that state, that is with a velocity and an energy of 1/2 m v^2, unless it finds something else to push on to cause it to stop. In everyday life we do not often come into contact with the resistance of an object to acceleration AND deceleration unless it is very heavy and very freely movable. Try picking up a long ladder in the middle so it is balanced and then turn round reasonably quickly (allow plenty of space) while you are holding it. You will very soon find out how hard it is to stop things that you have set in motion!
When Newton and Galileo formulated this in their investigation of things in motion it was considered to be very counter intuitive
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Well, yes, but that doesn't really explain why it doesn't stop moving as soon as you stop pushing it.
Why doesn't it? If there is no force acting against its motion, there is no reason it should stop.
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Frankly I feel a tad ill! My movements of mass have memory! That's just disturbing!
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I know about Inertia.. about objects temporaily melting together in contact, wearing each others movement down. But, lets take just one atom.. not even the whole atom, just the nuclei- and push that.. and lets take the smallest possible timescale, it flips from one position to the next. But why? I must somewhere store the memory that it was pushed.. (and it will have revenge for that bullying, it will became a uranium atom one day, blowing the world away)...
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I suppose one way of approaching this is to consider how many states an atom can be flipped into? If for the sake of argument it was two, then it would simply switch from one state to the other when force is applied. Therefore it would not require a memory.
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Precisely the same rules apply for the smallest subatomic particles in the Large Hadron collider (or any other particle accelerator for that matter) This is just a property of the universe, as I said before the "memory" is created while the particle is being accelerated and needs a reverse process to erase it.
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so this spin saves the state? So if i could alter that spin,i could create kinetic energy into any direction i want?
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Well, we have 'uniform motion' in space. That's a state where there is no resistance to motion, as long as it is free from gravitational influences. In fact there are only two states there, uniform motion and accelerations. So when you push something uniformly moving in space it has no weight, but it still has 'mass'. And that's what seems to be the reason for inertia, its refusal of changing 'motion'. When that inertia is overcome by your pushing you have introduced a new state, acceleration. That one will stay as long as you can give it a push. When you've finished pushing you also finished accelerating whatever you pushed on, and it now will go back to the state it had before, uniform motion. That uniform motion, and the one it had before, are just one state. Your push didn't differentiate it into two types, for example depending on 'speed'. It's one and the same and all experiments you do inside it will give you the same results.
So what happened with the 'push'?
You delivered some kinetic energy pushing, the box translated that into 'relative motion' dissipating some of it as heat as it overcome its inertial state of uniform motion. As you stopped it went back to the state all objects have on their own. Uniform motion. But some of that energy you delivered should now be stored somewhere, even though all uniform motions seems the same, don't you agree? And that's where the stress energy tensor comes into play placing it in the 'space' as I understands it.
The problem with that is that your uniform motion shows no sign of that storage, its atoms doesn't 'jiggle' any more. So what we have left is then the gravitational potential surrounding your box (the whole universe in a sense), and 'space' as such. So do your box now warp 'space' more than before? Not as I know. That leaves us 'space/the universe' that then somehow gets 'tensed' by the push, and/or your box new relative motion. Because we know that the energy that box will have interacting with some other matter will be greater after your push than before. So, the 'memory' you're discussing seems to be a result of a whole universe :)
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so mass is the reason for inertia? Or is mass the result of stored movement information? If i give it a different name, that doesent make it ex-plained out for a nub like me..
But how to hack that information ? Obviously gravity can, as it changes the ways things move, although its reach is limited, except of course that part of gravity that goes nuts and gets transported long distance to influence in disguise as dark matter..
I mean, i take a airless apple, it drops to the floor. Gravity changed its memory of movement, so if i could protect the apple from the information of gravity, it would be stuck were it is..
This Informationexchange does put things in a equilibrium, for example falling around a planet. Your Information to be dragged towards the planet is balanced out by your movement information of falling away-around the planet. So does the ISS shiver? on a microscopic scale it should, because the gravity field is not everywhere the same...
Do this information rays blur? Meaning the far-er away i get from a gravity-info radiating object, the more it stops fluctuating and becomes one constant(although small) dragging value?
Sorry if i spam your board with questions, but this thing really troubles me, its like a riddle, and you cant get rid, because everything you do, it is there, laughing in your face....
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!mater - why do you assume things should come to a stop? to rephrase in your terms - things do not need a memory of movement because the proclivity of everything to come to rest is not universal. On earth things come to rest because they are acted upon by forces (they run into a brick wall or lots of gas molecules) - but the natural state is unchanging. It is change that requires force - not continuity
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Indeed. If things were to naturally come to rest, then there must be some absolute standard for rest and motion. However, we have been unable to find this universal standard, we have only been able to find relative motion and acceleration.
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Then why does continued movement continue? Just because the universe always was that way, stop asking that question, that s no answer... i understand that stuff would in theory in open space would never stop moving (unless its own trail of darkmatter slows it down over time ;)
Sorry if this stubborness annoys you, but i always reacted to stuff i dont understand, using the brain as battering ram.
If you dont know, just say it..
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What makes you sure that any given thing is actually moving? How do you know that a particular object is not at rest?
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!mater. we can use the same physical laws and calculations(as physbang alludes to) to entities we judge to be a rest and those we judge to be in uniform motion. this is the reason we say that it is change that is the extra-ordinary thing, not continuity.
If you have two ballbearings - you fire ball G horizonatally from a gun and you drop ball D. The effects of gravity, cross winds etc apply equal to each - in fact you can set your frame of reference so that G is moving, or D is moving, or both are moving. thus we equate uniform movement with steadiness - as opposed to acceleration or change of movement.
slowing down is change of movement - an acceleration, this requires a force. Staying in uniform movement is the same as staying still and requires no force
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Staying in uniform movement is the same as staying still and requires no force
Exatamundo! So the body is exactly the same as long as it's not being shoved.
Ergo, a body that is not being shoved is no different from an identical body that was never shoved.
Ergo (obviously), all bodies that are not being shoved are stationary (not including paper clips).
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James Clerk Maxwell has two great arguments for "inertia"--Newton's first law of motion-- in Matter and Motion.
( http://www.archive.org/details/mattermotion00maxwiala )
ARTICLE XLI.—THE FIRST LAW OF MOTION.
Law I.—Every body perseveres in its state of rest or of moving uniformly in a straight line, except in so far as it is made to change that state by external forces.
The experimental argument for the truth of this law is, that in every case in which we find an alteration of the state of motion of a body, we can trace this alteration to some action between that body and another, that is to say, to an external force. The existence of this action is indicated by its effect on the other body when the motion of that body can be observed. Thus the motion of a cannon ball is retarded, but this arises from an action between the projectile and the air which surrounds it, whereby the ball experiences a force in the direction opposite to its relative motion, while the air, pushed forward by an equal force, is itself set in motion, and constitutes what is called the wind of the cannon ball.
But our conviction of the truth of this law may be greatly strengthened by considering what is involved in a denial of it. Given a body in motion. At a given instant let it be left to itself and not acted on by any force. What will happen? According to Newton's law it will persevere in moving uniformly in a straight line, that is, its velocity will remain constant both in direction and magnitude.
If the velocity does not remain constant let us suppose it to vary. The change of velocity, as we saw in Article XXXI., must have a definite direction and magnitude. By the maxim of Article XIX. this variation must be the same whatever be the time or place of the experiment. The direction of the change of motion must therefore be determined either by the direction of the motion itself, or by some direction fixed in the body.
Let us, in the first place, suppose the law to be that the velocity diminishes at a certain rate, which for the sake of the argument we may suppose so slow that by no experiments on moving bodies could we have detected the diminution of velocity in hundreds of years.
The velocity referred to in this hypothetical law can only be the velocity referred to a point absolutely at rest. For if it is a relative velocity its direction as well as its magnitude depends on the velocity of the point of reference.
If, when referred to a certain point, the body appears to be moving northward with diminishing velocity, we have only to refer it to another point moving northward with a uniform velocity greater than that of the body, and it will appear to be moving southward with increasing velocity.
Hence the hypothetical law is without meaning, unless we admit the possibility of defining absolute rest and absolute velocity.
Even if we admit this as a possibility, the hypothetical law, if found to be true, might be interpreted, not as a contradiction of Newton's law, but as evidence of the resisting action of some medium in space.
To take another case. Suppose the law to be that a body, not acted on by any force, ceases at once to move. This is not only contradicted by experience, but it leads to a definition of absolute rest as the state which a body assumes as soon as it is freed from the action of external forces.
It may thus be shown that the denial of Newton's law is in contradiction to the only system of consistent doctrine about space and time which the human mind has been able to form.
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sorry, been gone for a while.
And again, yes there is the perfect law of motion, and yes there is friction, and yes, it has been observed, and tested to death, and no, it doesent explain why stuff keeps moving. It just shows that you can calculate stuff moving, and that in a hundred thousand experiments it has been pr oven to death that it does so as stated in this law. However, a law does not replace reason. I googled and searched myself of course, with no real results.
I found a whole zoo of theory's on gravitation (mass, inertia and gravity being one happy family)
http://en.wikipedia.org/wiki/Category:Theories_of_gravitation
However, anything newer (new as in, post relativity-theory) drop fast into the arcana language of particle physics. Also, they reference to the Philosophers Stone of today (the Higgs-bosom), and how they will explain gravity with it, once they found evidence of it in CERN.
http://en.wikipedia.org/wiki/Special_relativity#Kinetic_energy
So if we can hack the Higgs-Bosson, i can get to the source of continued movement, gravity and inertia?
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You assume that there is some thing called rest, that this is the natural state of things, and that any deviation from this natural state needs some deviation. It seems that, in fact, uniform motion is the natural state of things and any deviation from uniform motion is the natural state of things.