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Post by Progenitor A on Oct 6, 2010 9:36:21 GMT 1
Hi again Carnyx
My this guy is getting excited!
He doesn't seem to want realise that if the angle of phase changes, then new frequencies pop up! So that if the phase angle of SHM changes, new frequencies, new periods are present.
If he were to read what is writ this might become clearer!
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Post by olmy on Oct 6, 2010 9:50:19 GMT 1
He doesn't seem to want realise that if the angle of phase changes, then new frequencies pop up! So that if the phase angle of SHM changes, new frequencies, new periods are present. Gibberish. Simple harmonic motion only involves one period - that is why it's useful as a clock, which, in turn, is why Carnyx wants the period to change with gravity (which it does for the pendulum but not for the spring). Oh, what's the point? What can anyone say in the face meaningless blather and a total refusal to listen...................?
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Post by Progenitor A on Oct 6, 2010 10:03:49 GMT 1
Gosh this guy is now fulminating!
In SHM, if the phase angle changes then new frequencies pop up - that's for sure - a physical fundanmental - admittedly it ceases to be SHM at that moment, but the fact remains How odd to argue vehemently against physical phenomena (freq = d(phi)/dt) and hence if a phase change occurse then new periods occur (phase modulation is a communications commonplace).
Still I am sure it helps his case to be abusive! At least he must feel sure of that!
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Post by olmy on Oct 6, 2010 10:37:18 GMT 1
In SHM, if the phase angle changes then new frequencies pop up - that's for sure - a physical fundanmental - admittedly it ceases to be SHM at that moment, but the fact remains Yes, if you suddenly physically interfere with SHO and change the phase, then all sorts of things happen and it is no longer a SHO or a useful clock for a while. This is supremely irrelevant to the pseudo-time dilation that Carnyx is trying to argue for because that would require two SHOs at different points in the gravitational field, having different periods. Still I am sure it helps his case to be abusive! At least he must feel sure of that! -shrug- You seem to think it is good for something............ There comes a point at which it is just not useful to argue with someone any more. It's always a difficult judgement because when people like you post rubbish, just as part of some bizarre ego trip of trying to make out that you know better than scientists, then people reading might actually get the impression you are right. Those of us that care about the truth and about people who might come here to learn, find it a little hard to just let that go. It is a serious shame that most science message boards have become places where those who actually know a little science have to constantly contend with scientifically illiterate wannabes who don't listen, people with chips on their shoulders the size of skyscrapers and those with religious or other agendas, who are intent on spreading their own disinformation for their own selfish reasons, with no regard for the truth or for those who may want to learn.... [/rant]
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Post by Progenitor A on Oct 6, 2010 12:42:50 GMT 1
When they are together, they will vibrate at the same frequency and so their phases will be the same. If you moved one of these 'clocks' to a different place where 'g' was different, (either millions of miles away, so as to reduce the 'g'' force, or by placing it in an accelerating reference frame .. such as a centrifuge..to increase the G force, you will find that its phase will change. In other words, this 'clock' will show a different time than the static one. If you simply ignore your fulminating critic who is by now getting apoplectic ,you are quite right, the vibrating spring surely does change as it is moved within a gravitational field. The reasoning is simple: We already know that time dilates as it is moved within a gravitational field. So as your vibrating spring is moved to a weaker field (or , in STA's terms, moved to a position of higher potential energy) then time will go faster. The spring, according to classical mechanical theory will resonate at apparently the same frequency, but whereas at the lower PE the period was 1/(t), at the higher PE the period is 1/(t'), where (t') is much shorter than (t); (remember that the 2nd order differential equations are solved wrt (t) or (t')) Therefore to an observer at the position of t, the spring will be vibrating at a higher frequency. Experimentally a 'blue shift' should be observable! PS, the changing phase constant (not constant whilst its changing of course!) does provide new frequencies and new periods, but this happens only during the change, so I think that a new value of phi, the phase lag/lead can be safely ignored!
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Post by olmy on Oct 6, 2010 13:10:13 GMT 1
The reasoning is simple: We already know that time dilates as it is moved within a gravitational field. ROTFLMAO! You really should pay attention, you know. Carnyx is trying to argue that time dilation can be explained by Newtonian mechanics...... Of course time dilation happens!
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Post by carnyx on Oct 6, 2010 13:36:17 GMT 1
Progenitor AThat link is really good, and should be required reading for Olmy olmyYou seem to think that I am saying that Einstein is 'wrong' ... whereas I am saying that you can deduce that a timer mechanism will run faster in an area with stronger gravity AND when they are accelerated, in a Newtonian world. Indeed Tong's excellent presentation ( HT to Naymissus) states this on the opening slide (i.e on page 3!) What I am saying is that clocks are merely counting mechanisms, but 't' requires a comparison between two counting mechanisms. And if you accelerate one counting mechanism and not the other, you will measure a different 't'. As indeed Tong shows. Now, this whole question of phase seems also to have eluded you. 'Phase' is a relative quantity, and like 't' requires the comparison between TWO counters. Take two sine-wave oscillators. When both are in-phase, i.e that the phase angle is a a steady zero, then both oscillators are are at indentical frequencies. If we speed up oscillator #1, and run it at a slightly faster frequency, we wil see the phase angle increasing continually. As you wil appreciate, there are now three frequencies we cna se,; F#1, f2#2, and the rotating phase angle f#3 which of course will represent the difference, which will also be a frequency. So, I hope you can see that when you talk about phase in the abstract; like 't', it is a relative quantity. (Oh, and I forgot; re your spring and weight analogy; what happens to the period of oscillation when you change the apparent mass?)
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Post by speakertoanimals on Oct 6, 2010 14:08:28 GMT 1
Well, it is unclear what she means by gravitational potential She could mean, as you say the potential energy of a mass in a gravitational field Or she could mean the definition of gravitational potential which is that force required to move a mass so that it is not affected by another mass's gravitational field There is similarity between the two, but also an essential difference. For example in the uniform gravitational field as STA has defined it( Constant accelerating force unrelated to distance) a mass can never escape the gravitational field of another mass and the gravitational potential is infinite. Of course in a real gravitational filed the amount of work needed to move a mass away from another decreases in proportion to the inverse square of the distance to be moved. However, assuming that STA means potential energy (which in a uniform gravitational field [as defined by STA] never decays as distance increases), here is a thought experiment Remember that STA maintains (I think) that time dilation is due to gravitational potential energy, and that is simply a function of a mass moving a distance against a restraining force. hence in a gravitational filed if identical masses are at heights h1 and 2h1 then one mass has twice the potential energy of another (and according to STA the higher mass has less time dilation than the lower mass) Now here is the thought experiment A simple square strong frame is constructed on gravity-free space(this experiment can also be conduced in a gravitational field). Two springs with clocks attached to one end are stretched and hooked to the frame. One spring is weak, the other strong. Both springs are stretched to the full extent of the frame. The potential energy of the strong spring is much greater than the weak spring. There is a big difference between their potential energies Does the clock on the strong spring run slower than the clock on the weak spring? First, I meant by gravitational potential what every basic physics text means by gravitational potential -- a function whose gradient is the gravitational field at a point. Hence zero of it undefined. What matters to time dilation is the DIFFERENCE in gravitational potential between the two clocks. Piffle. I can define the zero to be wherever I want, say at z=0. If I define the direction of z as the direction of the constant gravitational field, then I just have phi = gz. Which indeed goes to infinity as z goes to infinity, but who cares? I never said the constant field was constant over all space, just over some region. And since I was talking about the potential DIFFERENCE between two clocks both in the constant field region, that is finite. It is just convention that the zero of potential sometimes taken at infinity, then gravitational potential equates to energy needed to escape to infinity. For the constant case over all space, you can never escape, but again, who cares. This explains why toronto, in their rather simplified account, said it as they did. Because for a single gravitating body and a spherical solution (Schwarzschild solution in GR), then taking potential as zero at infinity, where spacetime is asymptotically flat, we define this as non-time dilated clock, in flat space. For closer clocks, the gravitational field strength is larger the closer you get, and the time dilation increases the closer you get. Hence could state it as -- the stronger, the more dilation, but this is a slightly misleading statement, it should actually be -- the lower, the more dilation, and since the field strength also increases the lower you get, the time dilation and the field strength both increase together in this case, BUT NOT IN ALL CASES. If we want to do a trawl through all uni physics websites, and a tally of how many times they make misleading statements, then feel free. but I'd rather go back to Einstein who derived the damn thing in the first place............. Not what Einstein said at all. What he actually said was that LOCALLY the effects of a (uniform) gravitational field and acceleration are indistinguishable. But once we are allowed to make non-local measurements (different directions of field strength, tidal forces etc), then we know we have gravity rather than acceleration, since acceleration can only mimic the effects of a uniform gravitational field . No I don't -- I said gravitational potential, which is the gravitational potential energy PER UNIT MASS. Hence GPE difference equals mass times difference in gravitational potential. Wrong. The gravitational potential goes as in the inverse of the distance, hence gives a force which goes as the inverse square. You should have said the work required to move something away by a further small amount (ie the force times that amount) goes as the inverse square, and made clear where you were talking about the TOTAL work to get from A to B, or the additional work to go from A to a bit further out. Or just used gravitational potential, gravitational potential energy, and gravitational field strength in the same way as everyone else.............. Since I never said it depended on GPE, but on gravitational potential.................... You also confuse the use of potential energy. The energy stored in the springs is REAL energy, a stretched spring just has more energy than an unstretched one. This total energy content contributes to the MASS of the spring, hence in one sense, a clock next to a stretched (hence more massive) spring will be time dilated compared to a clock say next to an unstretched spring, just as a clock sitting on the surface of a large planet will be time dilated compared to one sitting out at infinity. Except given E=mc^2, the additional gravitational effect of stretching a spring is too small a fraction of the unstretched mass for us to worry about this. Point is, what effects time is not just 'potential energy', but things that effect the shape of spacetime -- such as mass/energy.
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Post by olmy on Oct 6, 2010 14:45:35 GMT 1
olmyYou seem to think that I am saying that Einstein is 'wrong' ... whereas I am saying that you can deduce that a timer mechanism will run faster in an area with stronger gravity AND when they are accelerated, in a Newtonian world. Indeed Tong's excellent presentation ( HT to Naymissus) states this on the opening slide (i.e on page 3!) Poppycock. Page 3 simply gives the two Newtonian types of mass. What planet are you on? Now, this whole question of phase seems also to have eluded you. 'Phase' is a relative quantity, and like 't' requires the comparison between TWO counters. Take two sine-wave oscillators. When both are in-phase, i.e that the phase angle is a a steady zero, then both oscillators are are at indentical frequencies. If we speed up oscillator #1, and run it at a slightly faster frequency, we wil see the phase angle increasing continually. As you wil appreciate, there are now three frequencies we cna se,; F#1, f2#2, and the rotating phase angle f#3 which of course will represent the difference, which will also be a frequency. So, I hope you can see that when you talk about phase in the abstract; like 't', it is a relative quantity. None of this pointless waffle actually address the point that the frequency of the spring oscillator does not change with g. [This all being quite apart from the fact that has already been pointed out that time dilation does not need the force of gravity to be different, just the potential.] (Oh, and I forgot; re your spring and weight analogy; what happens to the period of oscillation when you change the apparent mass?) What 'apparent mass'? The oscillation period depends on the mass, the mass does not depend on gravity. You do know the difference between mass and weight, don't you?
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Post by carnyx on Oct 6, 2010 15:36:33 GMT 1
@sta ... Ever heard of Einstein's Principle of Equivalence? And since when has the discussion been other than about LOCAL gravitational effects? I repeat; Einstein says that it is not possible to distinguish between the force due to acceleration, and the force due to gravity. Please keep to the discussion in hand. You have defined a "rate-of-change-of-gravity-field" but you have not answered my actual question.How would you go about measuring, surveying and plotting, a gravitational field? olmyClearly you have lost you temper. Your spring-bob is a means of measuring 'g'. In a static state it can be used as an accelerometer. If you accelerate it; to the spring, the mass appears to have increased, and so stretches the spring proportionately. In a vibrating spring-bob, also used in accelerometer designs, applying an acceleration will result in a delay to the oscillation, and is seen as a phase-change. Increasing the acceleration will cause the phase to continue to change. So if you use two vibrating spring-bobs as counters in a clock system to measure 't' ... then the measured 't' will apparently change if one of the vibrating bob-counters is subject to changes in acceleration, or 'g'... and the other one is not.
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Post by abacus9900 on Oct 6, 2010 15:36:47 GMT 1
What she is trying to say is that the gravitation of the earth varies at different heights so that when defining a potential energy you consider the mass of an object, its height, and the force of the gravitational field (which is represented by the constant value 9.8 as the differences in the force of the gravitational field is negligible at various heights), i.e. potential energy = mass of object in kilograms x 9.8 x height of object in meters.
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Post by olmy on Oct 6, 2010 15:54:48 GMT 1
Your spring-bob is a means of measuring 'g'. You can use it to measure g but g only affects the equilibrium position, not the period of oscillation. T = 2 pi sqrt(m/k) See? No g. If you use the vibrating spring-bob as a counter as part of a clock system to measure 't' ... then measured 't' will apparently change if one of the vibrating bob-counters is subject to changes in acceleration, or 'g' and the other is not. Nobody is talking about one being subject to changes in g and the other not. Or have you suddenly decided that time dilation affects only those objects that jiggle up and down in a gravitational field, or something? Just out of idle curiosity, how do you explain time dilation due to relative (constant velocity) motion....?
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Post by Progenitor A on Oct 6, 2010 16:42:07 GMT 1
Well, it is unclear what she means by gravitational potential She could mean, as you say the potential energy of a mass in a gravitational field Or she could mean the definition of gravitational potential which is that force required to move a mass so that it is not affected by another mass's gravitational field There is similarity between the two, but also an essential difference. For example in the uniform gravitational field as STA has defined it( Constant accelerating force unrelated to distance) a mass can never escape the gravitational field of another mass and the gravitational potential is infinite. Of course in a real gravitational filed the amount of work needed to move a mass away from another decreases in proportion to the inverse square of the distance to be moved. However, assuming that STA means potential energy (which in a uniform gravitational field [as defined by STA] never decays as distance increases), here is a thought experiment Remember that STA maintains (I think) that time dilation is due to gravitational potential energy, and that is simply a function of a mass moving a distance against a restraining force. hence in a gravitational filed if identical masses are at heights h1 and 2h1 then one mass has twice the potential energy of another (and according to STA the higher mass has less time dilation than the lower mass) Now here is the thought experiment A simple square strong frame is constructed on gravity-free space(this experiment can also be conduced in a gravitational field). Two springs with clocks attached to one end are stretched and hooked to the frame. One spring is weak, the other strong. Both springs are stretched to the full extent of the frame. The potential energy of the strong spring is much greater than the weak spring. There is a big difference between their potential energies Does the clock on the strong spring run slower than the clock on the weak spring? First, I meant by gravitational potential what every basic physics text means by gravitational potential -- a function whose gradient is the gravitational field at a point. Hence zero of it undefined. What matters to time dilation is the DIFFERENCE in gravitational potential between the two clocks. Piffle. I can define the zero to be wherever I want, say at z=0. If I define the direction of z as the direction of the constant gravitational field, then I just have phi = gz. Which indeed goes to infinity as z goes to infinity, but who cares? I never said the constant field was constant over all space, just over some region. And since I was talking about the potential DIFFERENCE between two clocks both in the constant field region, that is finite. It is just convention that the zero of potential sometimes taken at infinity, then gravitational potential equates to energy needed to escape to infinity. For the constant case over all space, you can never escape, but again, who cares. This explains why toronto, in their rather simplified account, said it as they did. Because for a single gravitating body and a spherical solution (Schwarzschild solution in GR), then taking potential as zero at infinity, where spacetime is asymptotically flat, we define this as non-time dilated clock, in flat space. For closer clocks, the gravitational field strength is larger the closer you get, and the time dilation increases the closer you get. Hence could state it as -- the stronger, the more dilation, but this is a slightly misleading statement, it should actually be -- the lower, the more dilation, and since the field strength also increases the lower you get, the time dilation and the field strength both increase together in this case, BUT NOT IN ALL CASES. If we want to do a trawl through all uni physics websites, and a tally of how many times they make misleading statements, then feel free. but I'd rather go back to Einstein who derived the damn thing in the first place............. Not what Einstein said at all. What he actually said was that LOCALLY the effects of a (uniform) gravitational field and acceleration are indistinguishable. But once we are allowed to make non-local measurements (different directions of field strength, tidal forces etc), then we know we have gravity rather than acceleration, since acceleration can only mimic the effects of a uniform gravitational field . No I don't -- I said gravitational potential, which is the gravitational potential energy PER UNIT MASS. Hence GPE difference equals mass times difference in gravitational potential. Wrong. The gravitational potential goes as in the inverse of the distance, hence gives a force which goes as the inverse square. You should have said the work required to move something away by a further small amount (ie the force times that amount) goes as the inverse square, and made clear where you were talking about the TOTAL work to get from A to B, or the additional work to go from A to a bit further out. Or just used gravitational potential, gravitational potential energy, and gravitational field strength in the same way as everyone else.............. Since I never said it depended on GPE, but on gravitational potential.................... You also confuse the use of potential energy. The energy stored in the springs is REAL energy, a stretched spring just has more energy than an unstretched one. This total energy content contributes to the MASS of the spring, hence in one sense, a clock next to a stretched (hence more massive) spring will be time dilated compared to a clock say next to an unstretched spring, just as a clock sitting on the surface of a large planet will be time dilated compared to one sitting out at infinity. Except given E=mc^2, the additional gravitational effect of stretching a spring is too small a fraction of the unstretched mass for us to worry about this. Point is, what effects time is not just 'potential energy', but things that effect the shape of spacetime -- such as mass/energy. Thanks for the considered reply STA. I will now ponder on what you have said But before I do that what is meant by this sentence? Nay
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Post by carnyx on Oct 6, 2010 16:44:18 GMT 1
olmyALL measurements of 't' MUST consist of two counters, because it is a relative measurement. ALL real-world counters consist of detecting physical objects jiggling up and down in a gravitational field, as you put it, and counting those jiggles. Physical objects have mass, and there is no shield against gravity. Now taking STA's definition of a gravity field as a rate-of-change-of-g-field, and so a constant velocity trip in such a field will experience a continual rate-of-change of 'g'. And, a comparison between the counter of the traveller, and the counter of the observer back at base, will show an apparent change in 't' which will correlate with changes in the difference between the two local 'g's.
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Post by eamonnshute on Oct 6, 2010 16:50:00 GMT 1
ALL measurements of 't' MUST consist of two counters, because it is a relative measurement. Not true. The second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom. So you only need one counter.
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