Before getting to the topic of engine valves, it is necessary to discuss the relevant Theory.
When a Force is applied to a Mass, there is a thing known as "inertia" that must be overcome, for the Mass to begin moving. It happens that one aspect of inertia relates to the physical dimensions of the Mass.
As evidence, start by considering two one-ton steel objects. The first we shape into a sphere and suspend it like a wrecking ball. The second we shape into a long rod, say 100 meters long, and suspend it at multiple places along its length.
Now imagine a tall golf tee (say, a meter tall) with a golf ball on it. We want two. We push one tee into the ground at one end of that long rod of steel, and we push the other tee into the ground next to steel sphere. With both steel objects stationary, we want there to be a small gap (say, 1 millimeter) in-between each steel object and its associated golf ball.
Now the Test: Forcefully whack the two steel objects equally and simultanously, on the opposite sides from the golf balls. Because of the small gaps, each steel object must MOVE at least a little before it can knock its golf ball off the tee. That means the inertia of each object must be overcome before the golf ball can be struck by the moving object.
Well, if inertia depended ONLY on just the mass of the object, then both golf balls will be struck simultaneously. In actual fact, though, because the steel sphere has much smaller size than the steel rod, the sphere's inertia will be overcome first, and its associated golf ball will be knocked over first.
Now, how does that relate to engine valve "float"? First I need to describe what that is (those who know can skip this paragraph). When an internal combustion engine is run at very high RPM, the motions of the cylinder valves can start to fail to fully close, as if they were "floating" in a partway-open position. Engine performance deteriorates significantly when the valves start to float.
The most common design for an engine valve incorporates a short rod of steel. At one end of the rod is the valve-portion, that is supposed to seal the engine cylinder, and at the other end is an attachment point for a compression spring. The rod passes through the interior of the compression spring, on its way toward the engine cylinder.
Also at the attachment end of the short valve rod is a "contact" spot, where forces are applied to move the valve and compress the spring. Those forces cause the valve-seal end of the short rod to be physically pushed a small distance into the interior of the combustion chamber.
OK, per the Theory stuff above, it is necessary to overcome the inertia of the valve in order to make it move. If inertia depends partly on the length of an object, then the Simple Solution is to make the short valve rods even shorter!
One way to do that involves replacing the compression spring with a tension spring, so that the length of rod passing through the spring can be eliminated. More modifications to the engine are probably also needed, since "you can't do just one thing". But that one thing --making the valves shorter-- is the key, the starting point, for implementing this Idea.-- Vernon, Sep 13 2011 An internal combustion engine http://www.craftsma...eum.com/sealeng.htmThs page describes an engine-construction project, involving all the parts, including valves. Lots of pictures! Note that the valves of this engine are rather longer than in other engine designs. [Vernon, Sep 13 2011] Rarefaction Wave Gun http://www.dtic.mil...markAMikeBixler.pdfThe time it takes a force to traverse a distance IS relevant to affecting a mass! [Vernon, Sep 13 2011] National_20Protest_20Day [FlyingToaster, Sep 16 2011] Some discussion on Desmodromic drive Desmotrentadue_20RR_20V8 [normzone, Sep 16 2011] Drop and Stop Test Drop-and-Stop_20TestAs mentioned in an annotation. Various Standard Claims of Newtonian Mechanics need to be properly tested! [Vernon, Sep 17 2011] The Math http://www.rexresea...com/dean/davis4.htmFor [Ling] and anyone else who might be interested [Vernon, Sep 19 2011] // sphere's inertia will be overcome first //
May we enquire as to whether this test was carried out "in vacuo", or at STP ?-- 8th of 7, Sep 13 2011 [8th of 7], when talking about moving a ton of steel, the presence of a little air won't make any significant difference (unless the steel is shaped like a flat sheet and oriented to interact with lots of air).-- Vernon, Sep 13 2011 //Well, if inertia depended ONLY on just the mass of the object, then both golf balls will be struck simultaneously. In actual fact, though, because the steel sphere has much smaller size than the steel rod, the sphere's inertia will be overcome first, and its associated golf ball will be knocked over first.//
I'll retract my fishbone if you can provide a plausible reference for this statement. [-]-- Wrongfellow, Sep 13 2011 What I believe Vernon is trying to describe is the effect of the modulus of the long bar.
It is clear that if force is applied through a spring, the spring will compress and store some of the applied energy, thereby reducing the acceleration of the mass.
When calculating the properties of an IC engine valve train, the whole moving assembly and all it's properties must be considered. Among the subjects for consideration would be sealing at the valve guide, accurate location of the valve and wear in the valve stem / guide interface. It is these factors that lead to the requirement for long valve stems. Compression springs fit conveniently around these long stems.
The way to eliminate valve bounce or float is to use a desmodronic system, where a second cam pushes the valve closed instead of relying on a spring.
The gains available by reducing valve stem length are trivial. The delay between pushing one end and the other end starting to move is defined by the speed of sound in steel (which is, in turn, the result of the material's density and modulus).-- Twizz, Sep 14 2011 I agree with [Twizz] - any effect will be related to the speed of sound in steel, so there might be a microsecond or two to be saved between the 100m bar and the ball, but nothing wothwhile to be gained by making engine valves shorter.-- hippo, Sep 14 2011 [hippo], the speed of sound in steel is about 5000 meters/sec, so the time delay is rather longer than a microsecond when the distance is 100 meters. Logically, if you halve the length of a valve, however short it started, its new length can transmit force twice as fast as before.-- Vernon, Sep 14 2011 Beryllium: *very* high speed of sound. Maybe not for the valve face, but the body.-- FlyingToaster, Sep 14 2011 [Marked for deletion] Bad Science
The dimensions of an object have nothing to do with overcoming its inertia, inertia is a function of mass alone (rotational is another story, but not relevant here). Propagation speeds can matter, but only if the impulse is faster than the speed of sound in the object. Since the impulse for valve movement is generally not faster than the speed of sound in steel, even propagation isn't going to matter here.-- MechE, Sep 14 2011 If inertia is a problem, then you need to use lighter materials. Going back to your 1 tonne ojects, repeat the experiment with similarly dimensioned 100g objects, and you should notice a far superior response time for the same amount of force used to knock off your golf-balls.-- zen_tom, Sep 14 2011 Just out of interest: Speed of sound in steel 6100m/s Valve stem, say, 75mm Engine 6000rpm Camshaft 3000rpm Valve timing is late by 0.22degrees.
Probably the torsional flex in the camshaft is more than that...-- Ling, Sep 14 2011 Even if the speed-of-sound delay is significant (which I find very hard to believe), surely it's constant, at least when the valve has warmed up to its nominal operating temperature, and so the valve timing can be adjusted to compensate?-- Wrongfellow, Sep 14 2011 [-] I'm with MechE on this one.-- TomP, Sep 14 2011 I think I detect an attempt at humor here.
But desmo drive means Ducati, and that means cool sounding engines, so I vote for - Oh, that wasn't the idea, sorry.-- normzone, Sep 14 2011 [MechE], this is not bad science. Consider again that 1-ton 100-meter bar of steel. If you impact it at one end, you cannot possibly expect the other end to move instantly (faster than light!). Nor can you expect it to move at the speed of light. It is quite factual that it CANNOT move until the applied force reaches it, after propagating at the speed of sound in steel.
Meanwhile, the steel sphere is exactly as massive yet can physically respond faster to the same applied force, because it is smaller. You may not like the way I have lumped the time-delay of the long bar into the concept of "inertia", but remember that the main DEFINITION of "inertia" is "a property possessed by an object that must be overcome before it can begin to move in response to an applied force."
The time-delay associated with an object's shape must be "overcome" as certainly as its mass is part of the equation. It is just that most ordinary objects respond in less than a millisecond, so it is easy to assume that mass is the only factor of inertia that matters --and it isn't. Especially not when studying large objects, or extremely rapid events, such as engine-valve motion.
So, an engine valve is simply a smaller-scale version of the long-bar situation. However the force was applied to push the valve into the combustion chamber (cam or rocker arm), when that force stops the restoring force of the spring is there to affect the valve, and that force is being applied at one end of the valve. So the other end of the valve cannot BEGIN to close until that force propagates through the length of the valve.
[Ling], doesn't valve float typically happen at higher RPM than 6000?-- Vernon, Sep 14 2011 I imagine the "float" is a result of propogation delay in the spring at a macro level ie: the design of the spring, not at a molecular level. But the two are obviously related.-- FlyingToaster, Sep 14 2011 // If you push the end at less than the speed of sound, it will propagate at the speed of the push //
No, the motion will still propagate through the material at the speed of sound in that material. The observed motion at the free end will be at the same velocity as the impulse (if subsonic), delayed by the impulse transit time through the material.-- 8th of 7, Sep 14 2011 //"a property possessed by an object that must be overcome before it can begin to move in response to an applied force."//
That's not actually the definition of inertia, either. The definition of inertia is, simply, mass.
More specifically, it is the property of a given mass that causes it to accelerate less for a given net force.
You don't "overcome" inertia to make an object move. If there is an unbalanced force on the object it will move. You use inertia to describe how much it will move. In fact, if you remove any reference to inertia from the idea, I will remove my MFD, since the idea is about response speed instead of inertia in the first place.
And yes, inertia does affect response speed, because the restoring force is a given value, and it takes a given time for the restoring force to accelerate the valve enough to close it. However, that will be corrected entirely by decreasing the mass of the valve, or increasing the restoring force. The compression of the valve stem, due to propagation, which is what this idea depends on, is completely independent of mass (and therfore inertia).
As proof, consider your original example, but make the rod weigh one ton, or two tons, or three tons by increasing the diameter The propagation time for each of these is (allowing for variation in stiffness) identical. However, each rod will have a lower final speed (for an identical initial force, F/m=a), and that is a result of inertia.-- MechE, Sep 14 2011 8th, sorry I deleted that anno, because you are correct, and I misstated a couple of other things see later Anno for a better description.-- MechE, Sep 14 2011 [MechE], there are different definitions for inertia; mine is much closer to Newton's definition than yours. Because in the centuries since Newton, physicists chose to assume that mass was the only relevant factor. Except that it is provably NOT, when the length of an object most certainly is a factor (which is why I compared a sphere with a rod, and not similar shapes), with respect to it responding AS A WHOLE to an applied force!-- Vernon, Sep 14 2011 Vernon, Inertia is a bit of an issue since it doesn't have a mathematical definition as such, but my definition is the accepted one. Mine is also the exact Newtonian definition, so I'm not sure how yours is supposed to be closer. Mass is inertia, and inertia is mass.
There is no difference between the compression of a steel rod and a spring. Both fall under your definition, but are not inertial effects. The fact that a spring or rod in free space will compress under load is a result of inertia, but it is not part of inertia.-- MechE, Sep 14 2011 In addition, your sphere and rod will hit the golf ball at the same velocity and with the same force. If there were an inertial effect resulting from the geometry, that wouldn't be the case. Therefore there isn't.
I don't deny that you've hit on an actual idea, but describing it as inertial effect is bad science.
(There's also the fact that it's about 1/1000 of the total valve movement time and that if it were a major contributor it wouldn't be possible to prevent float through the use of positive displacement cams, which it is. Regardless, the idea is legitimate, but the theory is bad science.)-- MechE, Sep 15 2011 [MechE], it is exactly because inertia doesn't have a mathematical definition that reveals that those who specified the modern definition were not absolutely certain about it.
And it is most certainly a fact that EVERY solid mass, regardless of composition and quantity of mass, exhibits a time delay before ENTIRELY responding to an applied force --and that time delay is always related to the shape of the mass.
You might therefore be able to imagine just exactly why the concept of inertia HASN'T been defined with mathematical precision, when exacting measurements of very-differently-shaped yet-otherwise-identical masses can yield quite different "overcome the mass" times, if all those possible different shapes must be taken into account!
So, the time delay is usually ignored because it is so often quite small. But everyone acknowledges that time delays are most extremely relevant when an earthquake happens! And it happens that after a major earthquake happens, and its force has dissipated, the folks making precise measurements of the Earth's rotation can usually announce a slight change. In other words, the force of the quake affects the whole planet -- but not all at once.
All I'm saying is that that phenomenon should not be ignored with respect to ordinary objects, when there is a chance that that phenomenon is relevant to manipulating those objects. And the concept of "inertia" is simply the very-most-logical place to include that phenomenon, as part of the description of an object's properties.-- Vernon, Sep 15 2011 You could always do some math... 5k m/s, 6k rpm = sound will travel 50m through steel in the course of a revolution.
So (using say a 10cm valve stem) your propogation lag *would* be measurable, but it's less than a single degree of crank angle, so it wouldn't be responsible for floating the valve.-- FlyingToaster, Sep 15 2011 [Vernon] Yes, i'ts fair to say that valve float occurs at higher rpms, but nothing to do with your idea. Valve float is when the spring-driven closing of the valve cannot follow the camshaft profile because the spring FORCE cannot ACCELERATE the MASS fast enough. Did I mention inertia? Oh, yes, I just did.-- Ling, Sep 15 2011 //it is exactly because inertia doesn't have a mathematical definition that reveals that those who specified the modern definition were not absolutely certain about it.//
No, it is because there is no theoretical reason why inertial mass and gravitational mass should be identical, but they are. It has nothing to do with measurement error, they are identical.
//And it is most certainly a fact that EVERY solid mass, regardless of composition and quantity of mass, exhibits a time delay before ENTIRELY responding to an applied force//
A mass one atom thick exhibits no such delay.
Likewise, the first atoms in the object at the point of contact never exhibit such a delay. Both of these, however, do have inertial mass. And before you say it, yes the last atoms in an object do have a delay in responding, but that is because there is a delay in a force being applied to them. This is no different from a spring, and spring design is routinely calculated in precise detail, without resort to an inertial term.
//But everyone acknowledges that time delays are most extremely relevant when an earthquake happens!//
Yes, they do, but they don't describe it in terms of inertia.
I repeat, I am not arguing with your idea on theoretical grounds, but I am arguing with your definition of inertia. PROPAGATION TIME IS NOT INERTIA. Both have real definitions that do not overlap.-- MechE, Sep 15 2011 [MechE], DON'T put words in my mouth! Read the main text: "Well, if inertia depended ONLY on just the mass of the object, then both golf balls will be struck simultaneously." I most certainly have NOT been saying that the time delay is all there is to inertia. I'm saying it is a valid COMPONENT of the concept. Mass is indeed still the major component.
By the way, even a single atom still has time-delay under ordinary conditions. I'm told that when one atom collides with another, the electron clouds surrounding both get squashed a bit, until the mutual repulsion of the two nuclei actually transmits the force from the first to the second. Well, the squashing process takes time...not a lot, but some. I will, however, agree that for certain subatomic particles, such as electrons, the rules of Quantum Mechanics can occasionally allow them to experience Zero time-delay when doing some things (quantum leaps between orbits, for example).
[Ling], The force of the spring can't accelerate the valve mass AT ALL (discounting stretching) until AFTER the force propagates to the far end of the valve. I can agree that reducing the mass can help the situation (but all those auto mechanics already know that). And so I have focused on valve length, because reducing it will also help. (Not to mention, of course, that a reduced length will also probably reduce the valve mass.)-- Vernon, Sep 15 2011 //[Ling], The force of the spring can't accelerate the valve mass AT ALL (discounting stretching) until AFTER the force propagates to the far end of the valve.//
Sorry, Vernon, that is so wrong. That's like saying a long spring can't be pulled AT ALL until the far end sees the tension.
I think you are saying that the apparent instantaneous inertia appears to be lower if something is longer. That could be shown by pushing a large lump of jelly. At first it just squashes and the far bit doesn't know until the pressure wave gets there. But after the impulse settles down, and the force is maintained, then everything appears as normal.-- Ling, Sep 15 2011 Don't put words in my mouth either. I said they are two completely independent concepts, and you are trying to combine them.
At no point did I say you were excluding true inertia from the definition.-- MechE, Sep 15 2011 This could be a boon to players of the French horn.-- MaxwellBuchanan, Sep 15 2011 [Ling], I was describing properties of engine valves, not the springs, and so I specifically said ("discounting stretching)", because they are made of stuff that is quite hard --after all, you did specify in an earlier anno a speed of sound of 6100m/sec, when I had stated a figure (good for most ordinary steels) of 5000m/sec. Harder materials propagate sound and mechanical forces faster (with diamond being so hard that even thermal vibrations can be conducted like sound waves). But harder materials also stretch less!
[MechE], I didn't put words into your mouth. The context of your statement "propagation time is not inertia" indicated that you seemed to think I was claiming that it was. Nope, I'm saying there is reason to include it in the overall definition of inertia, along with mass. Because the overall movement of a mass DOES depend partly on the propagation time, and inertia is the "property" of a mass that must be overcome to get it to change --as a whole-- its current state of motion.
The above logic is more ironclad than the conventional definition, which implies anything can respond to an applied force in zero time, not just elementary particles. Tsk, tsk, seismology disproved that notion long ago. (I put "property" in quotes because it properly needs to be divided into two properties.)-- Vernon, Sep 15 2011 Vernon, Propagation time is not inertia, it is not a component of inertia, it has nothing to do with inertia.
Note that none of that implies that I think you said it was the entirety of inertia.
Inertia is not something that needs to be "overcome" which would imply there is some net force which will cause no motion. Any net force will cause motion, just not as much for an object with a higher inertial mass.
//Because the overall movement of a mass DOES depend partly on the propagation time//
The overall movement of a mass also depends on young's modulus, friction, electrical charge, gravitation, dozens of other factors, but no one tries to lump them in with inertia.
//I put "property" in quotes because it properly needs to be divided into two properties.//
It is, inertia and propagation time. As you yourself point out, propagation time is nothing new, it is well understood, in earthquakes, in high speed actuators, etc. etc. That does not make it an inertial effect. You say it is:
//It happens that one aspect of inertia relates to the physical dimensions of the Mass.//
This is wrong, and bad science. There is nothing else that can be said about it.-- MechE, Sep 15 2011 Oh, like I could resist that opportunity.
"Desmo, desmo, desmo" he cried.-- normzone, Sep 15 2011 vernon has this thing about the way energy moves in solids. its wrong, mind you, but we should let him have it. Valves float because designers use soft springs and heavy valves and quick camshafts. With only minor modifications the valvetrain on an OHC engine may be turned to almost any speed desired with the resultant losses in valve opening, friction and expense in materials.-- WcW, Sep 15 2011 [MechE], show me where, in Standard Mechanics, the propagation time is NORMALLY included in the calculations, the same way those other factors you mentioned are normally included, when describing how an object responds to a force? Because it mostly isn't, and that's what I'm trying to correct!
The Wikipedia article on the subject starts out like this: "Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass." The article does NOT insist that mass is the ONLY aspect of inertia that matters. As an analogy, suppose I stated that the force of Gravitation between two objects was proportional to their masses? I would be both perfectly correct and perfectly incomplete.
And so I'm saying that the standard definition of inertia is incomplete, that the propagation time should always be included in the calculations, simply because PART of any object will always utterly ignore an applied external force, UNTIL the force propagates through the object to reach that part of it! And THAT counts as "resistance" (as used in the Wikipedia article) to me. If it doesn't count as resistance to you, well, consider it to be an oversight in the Standard Training given to mechanical engineers everywhere.
[Wrongfellow], since I'm right, about the need to always include the propagation time if you want to accurately describe the overcoming of an object's resistance to an applied external force, I'm not talking about Bad Science. Which is why I will keep deleting your attempts to shut me up on the subject. You can shut me up by proving me wrong, which YOU certainly haven't tried to do here. But shutting up a debate opponent any other way is pure cowardice, plain and simple --an attempt to ignore/bury facts that would force you to admit you were wrong.
[normzone], whatever-it-is to which you referred, it is unfamiliar to me. Could you explain, please?-- Vernon, Sep 16 2011 //propagation time should always be included in the calculations//
Both [Ling] and myself did it for you and both of us calculated out much less than a single degree of rotational delay due to molecular lag, ie: it's not what's causing float.
You're Welcome.
And you have no reason to speculate that engine designers *don't* include it in their calculations... I sortof assume that they do.
I also assume that the conditions that cause floating valves are not within the normal operating parameters for the engine; indeed that the designers decided that the extra stuff needed to allow the engine to operate at those speeds would be at the expense of performance that *is* within the normal operating parameters.
Propogation time is not something that's routinely ignored in science or mechanics: anything with the word "audio" includes formulae or at least rules-of-thumb regarding acoustics, and that includes not only musical instrument design and rock concert and recording acoustics (which is quite complex) but architecture.
Propogation time in solids is an entire chapter in aircraft design.
Computing hardware design.
Radar.
Sonar.
Is there something seasonal about this disagreement you have with Newton ?-- FlyingToaster, Sep 16 2011 [FlyingToaster], thank you. I'm quite willing to agree that the mass of the valve is a major cause of float, so long as all of you agree that the length of the valve is also a factor. And so, the Idea here about shortening the length of the valve, IS valid (two ways, as mentioned in a prior anno).
Some of those propagation times you mentioned have nothing to do with the propagation of mechanical forces. And the problem I have with Newton is that his basic equation (F=m*a) assumes that the propagation time is always exactly zero.
Remember that Newton has been not-accurate-enough twice before in the History of Physics, which is why we now have Theories of Relativity and Quantum Mechanics. Why can't Newton be not-accurate-enough again?-- Vernon, Sep 16 2011 // when talking about moving a ton of steel, the presence of a little air won't make any significant difference //
I beg to differ; my Duece is made from approximately seven tons of steel, and a tiny little bit of air in the wrong place (or escaping from the right place) can halt its movement altogether.-- Alterother, Sep 16 2011 or force you to rely on the 4-5 vehicles in front at a stoplight for halting.
("yes sir, you say the offending vehicle climbed over 5 cars first before plowing into you, then roared off into the night ?")
[V] N's formulae are maths for the purpose of maths; you want the aisle rather clearly marked "engineering formulas".
<link>-- FlyingToaster, Sep 16 2011 // or force you to rely on the 4-5 vehicles in front at a stoplight for halting. //
Nearly been there, nearly done that. You might be surprised how many hatchback drivers don't seem to notice they've cut me off until my front differential is filling their rear-view mirror. As punishment for their carelessness, I like to roll up so close behind them I can't actually see them over the hood. By that time, of course, my customized 4-tone air horn has turned their internal organs to jelly. Ya gotta love locomotive graveyards.
Sorry. I like to brag about my truck.-- Alterother, Sep 16 2011 Even with propagation, F still equals MA. The force takes a fraction of a second to propagate, but every particle of the mass accelerates exactly proportional to it's mass and the net force it experiences.-- MechE, Sep 16 2011 [MechE], yes, that's the standard CLAIM. But has it been put to the test? Consider what the mass is doing WHILE that force propagates through it --is each subunit of the mass accelerating (experiencing a rate-of-change of velocity), or is it experiencing a rate-of-change of Acceleration, from zero up to its final "official" value?
Some time ago I proposed a way to test it, to be sure. See "Drop and Stop Test" link.-- Vernon, Sep 17 2011 // is each subunit of the mass accelerating //
How small is this "subunit" ? That needs to be clearly defined as you are straying into the boundary region between macroscopic and quantum effects.-- 8th of 7, Sep 17 2011 vernon never strays.-- WcW, Sep 17 2011 [8th of 7], good question. "Whole atoms" is probably the most logical answer, because although they most certainly can exhibit QM behavior, they also can exhibit some classical Newtonian behavior (billiard-ball collision stuff). However, we probably need to include some volume of space about each atom, and not just the atom only, so that overall motion of the atom can be considered. We don't want to ignore such things as its normal vibrations when at room-temperature.
When an object experiences a common impact-type of force, at the instant the force is applied, only the atoms at the surface of the object begin to accelerate. These push on neighboring atoms, and their behavior is what we want to study. I already mentioned in a prior anno something about electron clouds getting squashed, a process that takes a bit of time....
[WcW], you would prefer I be inconsistent, the better to denounce the stuff I say? Too bad!-- Vernon, Sep 17 2011 vernon you have posted this idea repeatedly (six times?).-- WcW, Sep 17 2011 do you have any specific examples of situations where inertia depends on object length?-- WcW, Sep 17 2011 Oo er mises!-- pocmloc, Sep 17 2011 Let's assume that inertia changes according to an object's shape. What wonderful effects should we get?
An object could be accelerated in one orientation, and decelerated in another. If this were done often enough it would consume energy without trace.
Speed of sound in object would depend on the overall shape. Propagation depends on acceleration of the "sub- units" which somehow know the length of the shape in every direction, and change their inertia to suit.
Different density objects would accelerate at different rates in a gravitational field. Lower density is longer for the same mass so a gas planet would have more inertia than a similar mass solid planet, meaning they would have different orbital radii.-- Ling, Sep 17 2011 [WcW], I presented an example in the main text, involving two one-ton steel objects having different shapes. Didn't you read it?
[Ling], some of what you wrote is incorrect. In a gravitational field all parts of an object are subjected to the field; the force is not applied to a point such that it propagates from that point through the object. (If an object was big enough for tidal effects to be significant, you STILL have all parts of the object being subjected to gravitational forces simultaneously; only the DIFFERENCES in those forces need be considered as propagating through the object.)
And, no, the speed of sound in an object depends only on the substance of the object. The propagation time depends on the speed of sound and the shape. The subunits of the object DON'T change their inertia at all; they merely get affected when the wave of propagating force reaches them, and NEITHER sooner nor later. How are you reaching different conclusions?
Regarding your first item, about "consume energy without trace", no, the math was worked out in the early 1960s and the guys who did that math assumed that some energy would be radiated from the system, analogous to what is known about electromagnetic waves being radiated from an electromagnetic system that is subjected to various nonsimultaneous manipulations.-- Vernon, Sep 18 2011 Somehow you are proposing that the subunits don't change their inertia, but the whole object does, and furthermore the object changes it's inertia depending on the total shape. If I reduce to two subunits, side by side, then each has the same inertia, but together the inertia is not equal to two? The difference is radiated as some kind of electromagnetic wave.
Is that a fair summary?-- Ling, Sep 18 2011 [Ling], since atoms are spherical, it is perfectly reasonable to expect any one of them to always take the same amount of time to respond to an impact-type of force.
Next, remember that for all stable atoms heavier than Helium 3, the nucleus outmasses the electron cloud by more than 3600-to-one (every proton is accompanied by a roughly-equal-mass neutron --and heavy atoms like lead can have 1.5 times as much mass-of-neutrons, compared to the mass of protons). So when one atom collides with another, it is perfectly reasonable that the clouds get squished.
Which means that if two atoms are lined up and the first gets struck, then we get some action somewhat equivalent to billiard balls (moving nuclei), and so time must pass between the first atom getting struck, and it making the second one move. It should be obvious that if the were side-by-side and both were struck simultaneously, both would be receiving the applied force simultaneously.
PLEASE keep in mind that I'm saying that the time delay is (or should be) only PART of the overall definition of inertia. It certainly is small enough a factor that under ordinary conditions (humans interacting with stuff), only the mass is noticed, not the time delay.
Finally, re-read what I wrote in my last anno: "some energy would be radiated from the system, analogous to what is known about electromagnetic waves" --I didn't say the radiation WAS electromagnetic (the guys to did the math say the waves should be gravitational).-- Vernon, Sep 18 2011 So your proposal is more like "When atoms are pushed together they radiate gravitational waves". I presume that if this is the case, you say that energy is radiated in the case of an object subject to a fast acceleration, and so the object does not achieve the speed that it would otherwise have attained? Hence the apparent increase in inertia...
So, there are other ways that atoms are pushed together...
When an object is heated, it will radiate gravitational waves? That would decrease the apparent temperature.
Or when an object slides, the friction creates gravitational waves?-- Ling, Sep 19 2011 [Ling], my proposal is that they should make engine valves shorter, not JUST less massive, so they can respond faster to the forces applied to them (from cams and springs).
The explanation as to why gets into proposals made by other folks, which I'm simply repeating here. It is THEIR math that led them to conclude that gravitational waves can be emitted by masses that are experiencing not just accelerations (Einstein did that already, and most-extremely-feeble are usually THOSE grav-waves), but changing accelerations (a.k.a. "jerks").
If you don't have a situation involving significant rate-of-change of acceleration (most "friction" situations), then you don't have significant gravitational radiation. And most of Newtonian Mechanics is NOT about changing accelerations, because such are usually too-short-duration to bother with. That is, changing accelerations would be happening only during the short propagation time, while an impact--type force propagates through an object (often less than a millisecond).
Only in situations where jerks happen repeatedly do physicists SOMETIMES bother to do the extra math. Bot obviously not often enough, since the subject is still controversial!-- Vernon, Sep 19 2011 But friction is described by one famous physicist as "Snap, jiggle". Those are impulses at the level of subunits that you are talking about, therefore friction should radiate gravitational waves according to your proposal.
When objects are hot, the subunits are continuously banging into each other, are they not? That should also cause the radiation of gravitational waves according to your proposal.-- Ling, Sep 19 2011 Errr, actually, they do.
It's a reductio-ad-absurdum argument, but gravitational attraction is a function of mass. The actual size of the mass is unimportant, and can be taken down to the atomic level.
Theoretically, two hydrogen atoms, all alone and out in deep space exert a gravitational attraction on one another. The fact that said force is vanishingly small is irrelevant; it is there. By moving one of the atoms towards and away from the other, the force between them will increase and decrease according to inverse square law. This is a "gravity wave".
So [Vernon] is actually correct; it's simply that the forces involved are at or below the limit of detectability, and at atomic-scale distances are swamped by the elctrostatic force and the Strong and Weak nuclear forces.
Because in a hot object the motion of the individual atoms is chaotic, the average gravitational force exerted on an external mass is zero. If the atoms were all moving in phase and in the same plane, then it would still be an effect at the limits of detectability.-- 8th of 7, Sep 19 2011 OK, so I'll put together what you and Vernon are saying, and play around with it:
[Vernon]//Finally, re-read what I wrote in my last anno: "some energy would be radiated from the system, analogous to what is known about electromagnetic waves" --I didn't say the radiation WAS electromagnetic (the guys to did the math say the waves should be gravitational).//
[8th o f7]//Because in a hot object the motion of the individual atoms is chaotic, the average gravitational force exerted on an external mass is zero. If the atoms were all moving in phase and in the same plane, then it would still be an effect at the limits of detectability.//
Then it seems that energy is radiated through "gravity waves" for some interactions, but then absorbed again by other interactions. In Chaotic motion the balance is pretty much zero. Vernon is saying that with an organised impulse, it is non-zero.
My comment on the impulse: it has a leading and trailing edge of pressure and rarefaction. Let's say the leading edge causes a net energy radiation (emmission), using Vernon's idea. How does the trailing edge re-absorb the energy radiation? Or doesn't it? If the radiation is really, er, "radiated", then it isn't coming back and cannot be re-absorbed. That would mean that mass is reducing...
But if it were treated like a magnetic field, then the gravity field could be built up and collapsed. But then, how is it correct to say that it is radiated?
Extrapolating wildly, it seems you are proposing [putting words into your mouth, Vernon] that the impulse creates a change in the gravitational field of the object, which temporarily stores some energy and releases it back into the object when the impulse passes.-- Ling, Sep 19 2011 [Ling] That is exactly what Vernon has stated elsewhere. That rapid change in acceleration somehow emits "gravity waves", which I would interpret as a slight and temporary increase (or decrease) in the gravitational mass of the object.
[8th] This would not be the objects gravitational mass or the resulting force, this would be energy expended to temporarily change said force.-- MechE, Sep 19 2011 // energy is radiated through "gravity waves" //
Force is transmitted by gravitational wavicles. Energy is only involved if a mass moves with or against such a force (= "work").
To be more concise, the net change in gravitational force produced by thermal movement of individual atoms averages out at zero. Obviously, the overall gravitational attraction exhibited by the mass is non-zero; but is (on a macroscopic scale) unvarying.
// Choatic //
Sp: Chaotic
// Vernon is saying that with an organised impulse, it is non-zero //
It is non-zero only when all the atoms in the structure move synchronously in the same direction. A shock-wave propagating through a material merely causes its constituent atoms to oscillate about a fixed point.-- 8th of 7, Sep 19 2011 Aharrtrr!-- MaxwellBuchanan, Sep 19 2011 Prove it. Seems like this is middle school science fair material. I propose that you set up a jig with a cam and a spring and demonstrate that a long object will overwhelm a spring before a short object of the same mass. What are you afraid of.-- WcW, Sep 19 2011 // What are you afraid of. //
Tribbles.-- 8th of 7, Sep 19 2011 [Ling], I hadn't heard that definition of friction before. OK. But for most objects the amount of mass (at the surface) being snapped is so small in comparison to the whole mass, which is NOT being snapped, that we shouldn't expect to measure much energy loss via gravitational waves, especially when it can be hidden by so much that gets converted to heat.
[8th of 7], you are describing the waves that Einstein first described, related to the simple acceleration of masses. And, yes, those waves are quite feeble even when the masses are as large as, say, Jupiter. Else such radiation would have decayed planetary orbits MUCH more than has actually happened in the last several billion years. But the gravitational-radiation-caused orbital decay of binary stellar-mass pulsars IS significant and has been measured
I've linked an article that contains the math I mentioned in prior annos. The claim is that gravitational radiation associated with rate-of-change of acceleration is rather greater than that associated with simple acceleration --but still extremely weak and difficult to detect. I know of some additional math that points out the ratio of Energy to Momentum of a gravitational wave can be VERY different than that ratio is, for electromagnetic waves. So, a low-energy grav-wave could carry quite a bit of momentum --but it is the energy that we typically seek to detect, with respect to measuring either loss or absorption.
[Ling], the absorbability of those gravitational waves is not a matter that needs to be mentioned, if, as in the friction example, the amount getting radiated is trivial. Also, a "wave" in a solid substance consists of BOTH the compression and the rarefaction (like the crest and the trough are both part of a surface wave on water). I have no reason to think that only part of that activity in a solid is connected to the radiation of a gravitational wave.
[MechE], I've simplified some of what the linked article states, since the author claims that the wave of mechanical force must propagate from near-end to far-end AND BACK, before the object-as-a-whole can respond to an applied impact in the Newtonian manner. I quote: "No matter how much force is applied, the center of gravity of the rod cannot obey F=Ma in less than this time. It would be oversimplifying to say that the rod acts as though it had infinite mass during this time, since the center of gravity will be moved somewhat by compression, but for all practical purposes, the rod acts as though it had a much larger mass than it actually has." And so I have taken the liberty of calling that effective temporary mass-increase as "a factor that should be included in the definition of inertia".
[8th of 7], to what extent can you be sure that simple thermal vibrations include rate-of-change of acceleration, and not simple acceleration? Because if only simple acceleration is involved, you won't see any of this type of gravitational radiation.
[WcW], your description could be better, but I catch the gist of what you are saying. Too bad I haven't got any money to spend on that project --or other projects that I've been wanting to do for years.-- Vernon, Sep 19 2011 //The claim is that gravitational radiation associated with rate-of-change of acceleration is rather greater than that associated with simple acceleration//
It's deja vu all over again...-- MaxwellBuchanan, Sep 19 2011 [MaxwellBuchanan], if there were lots of places in Physics where the consequences of jerk couldn't be ignored, then Physics wouldn't have ignored it so much, right? So, if I happen to encounter a few worthy places, like the valves in an internal combustion engine, where jerk can be a significant factor, I see no reason to avoid mentioning it.-- Vernon, Sep 20 2011 I really don't think testing this would cost more than 50$-- WcW, Sep 20 2011 Physics (and engineering) don't ignore jerk. Ignoring something means you change the equations to neglect it. This is frequently done for something like gravity, where g=9.81m/s^2 is substituted for g=G m1 m2/r^2 (which is substituted for the even more complicated version that doesn't treat the earth as a point mass. The reason is because the variation is so minor for most uses.
Jerk just doesn't show up because it's inherent in the equations of motion without requiring a specific term.-- MechE, Sep 20 2011 [WcW], then you do it. The next loose $50 I see HAS to be saved, for replacing a dying refrigerator.
[MechE], exactly where in the standard equations is the thing that engineers call "the starting transient"?-- Vernon, Sep 20 2011 Ah, there's the simplifying assumption, and it's not Jerk. It's propagation time (note that these are not the same thing). I never consider propagation time in my designs, I admit it. Why? Because I'm dealing with moves that happen in tens of milliseconds at the shortest, not tens of microseconds. I do occasionally allow for settling time, which is a function of the same thing, however.
Even for the valve, as discussed above, the propagation time is 1/1000th of the normal move, and thus is probably not worth considering. Especially since many other factors, primarily friction and heat are going to be much bigger factors.
It would not surprise me, however, to know that automotive engineers do take it into account, I'l admit I don't know any. I know every rocket propulsion and turbine engineer I personally know do. I personally discussed it during an interview with a company making guidance systems for artillery (for some reason they didn't have to take gravity waves into account to hit their targets). I likewise know that FEA programs doing transient and vibration analysis exist essentially to deal with this. This is not some new thing you have discovered that changes the world, it is a minor factor that is accounted for in extreme environments and ignored when it is not needed.
Jerk, on the other hand, is the rate of change of the rate of change of the rate of change of the position of an object. If you graph the position of an object with respect to time, that information is there. If you construct equations that describe that graph, the information is included in those equations without adding a specific term.-- MechE, Sep 20 2011 [Vernon], I think this has already been done. Remember the guy working on the reactionless drive? Who was looking for investors and would provide a demonstration of his cunning device? And who was unable to provide a demo when I offered to invest, because he had someone already who might be interested? And who was still "in discussion" several months later when I emailed him again? And who has not got back to me? Well, obviously he hasn't got back to me _not_ because his device doesn't actually work, but because he's had a huge investment and will, no doubt, be flooding the market with devices exploiting this new and remarkable law of physics.
I mean, obviously.-- MaxwellBuchanan, Sep 20 2011 [MechE], I ask again (quoting an earlier anno), "Consider what the mass is doing WHILE that force propagates through it" --you cannot possibly say it is all accelerating at once, if the far end holds still until the force reaches it! I fully agree that in many circumstances jerk can both be present and be ignorable, simply because the propagation time is so often so short (can apply to cannon-shells, see?). But that doesn't mean, when you decide to include jerk, that you must mess with it independently of the propagation time. I suppose I should ask what rationale is there for keeping the two separate, when it actually could be MORE convenient to tie them together, as in (F=mjt) --it should be obvious that if "t" is small enough, then "F" can be ignorably small, too, a tiny part of the normal (F=ma).
[MaxwellBuchanan], it's been long enough that it might not be inappropriate to ask the fellow about the status of his investor situation. Meanwhile, it remains true that the devices described online are basically operating at mechanical frequencies, not electronic frequencies, and the equations, should they prove to be correct, say that the device will never really be efficient at mechanical frequencies. So (again with correct math) even if the thing works, I don't expect it to be so practical as to become widespread --and it might cost a lot of investment to finally admit that the math is right about that!-- Vernon, Sep 21 2011 Jerk is indenpendent of propagation time, I'm not "messing with them". As I said, jerk is included in the equations (although not as a separate term), propagation time often isn't. Propagation time is a simple equation F(at point x)=f(at zero) *x/(speed of sound in the material) *t. Admittedly it can echo, which makes it more complicated, but please tell me where in there jerk comes into play? (you can back solve acceleration out of the force terms, but not jerk)
Let me repeat JERK IS NOT IGNORED, it is subsumed. There is no need for a specific term in the equations of motion for it, because there is no outside actor that acts dependent on jerk. Instaneous acceleration is sufficient for determining maximum loads and similar. (spring forces are dependent on positon, wind resistance is dependent on velocity, force is dependent on acceleration, nothing is dependent on jerk)-- MechE, Sep 21 2011 To further clarify, you're right, propagation time is frequently ignored, but the net result of propagation time is not a force. If you push a one atom thick sheet or a one atom diamter rod of the same mass, with the same force the final velocity of the objects will be the same. There is no term in the equations of motion (nor should there be) that change that. If you don't believe me, get a lead rod and a lead ball. Hang them as described in your initial annotation. Hit them with a calibrated force observe them with a high speed camera and let them hit a precision load cell.
It may take the rod a fraction of a fraction of a second longer to reach the cell (I'm not actually sure of this, because I have a sneaking suspicion that the net accleration is constant, but anyway...), but it will be moving at the same velocity when it does, and it will hit with the same force. This elminates the possibility that propagation time can be considered an inertial effect.
Let me repeat that I have never said that shorter valves (or equivalent) will not have a lower propagation time, but I (and physics) stand by propagation time not being, in any sense, an inertial actor.-- MechE, Sep 21 2011 //JERK IS NOT IGNORED, it is subsumed.// I think [8th] should have some insights on that one.-- MaxwellBuchanan, Sep 21 2011 [MechE], I think you will find that when an impact physically/permanently deforms an object, jerk will be a major part of why it happens. Of course, most objects are expected to resist permanent deformation under ordinary impacts, so again jerk gets to be mostly ignored.
You didn't answer my question. OK, I didn't phrase it as a question, so now I will: "What is the mass doing WHILE an impact- force propagates through it?"-- Vernon, Sep 21 2011 //jerk will be a major part of why it happens//
How? Maximum acceleration, yes, since that determines/is determined by the maximum force, but the change in acceleration (jerk) has no effect, only the peak acceleration.
//"What is the mass doing WHILE an impact- force propagates through it?"//
It's compressing and spreading outwards, exactly like any object under any load. What's that got to do with anything?-- MechE, Sep 21 2011 [MechE], perhaps I didn't sufficiently point out the importance of the Question. Please keep in mind that the very ordinary DEFINITION of a Force requires a Mass to be Accelerating. Well, if we know that we have APPLIED an impact-type Force to a Mass, but it is NOT instantly Accelerating-as-a-whole, then exactly WHAT is the MASS (not the object) doing, during the propagation time of the Force throughout the Mass?
I agree that the compression/spreading you mention (for the OBJECT) logically follows from the fact that the propagation of an impact-type Force is as a compression wave. Why doesn't it ALSO logically follow that the Mass-as-a-whole can be described as experiencing jerk DURING that propagation, especially when we know that (A) BEFORE the Force started propagating, its Acceleration was Zero, and (B) AFTER the Force finishes propagating, the whole Mass will be Accelerating at some non-Zero rate? (Let us assume that the initially-applied impact-type Force is still being applied, throughout the propagation time. There are situations where this is known to occur, such as when a golf ball is struck during a normal golf-club swing.)
The preceding is why I'm convinced it should be generally recognized that the Mass experiences a rate-of-change of acceleration ("jerk") during the propagation of a Force through it. And, so far, you have not explained why that cannot be a correct description.-- Vernon, Sep 22 2011 Perhaps it might help to picture the mass as a series of small masses connected by springs (an analogy which pretty well describes the interaction between molecules in the mass).
When a force is applied, the first small mass is initially accelerated according to F=ma. As it begins to displace, it compresses the spring connecting it to the next small mass. This exerts a force on the second small mass, causing it to accelerate. The force from the spring is reacted against the first mass, opposing the input force and reducing acceleration of the first mass. This is the mechanism by which the force propogates through a mass, the rate of propogation being a function of the density (mass of each of the small masses) and modulus (rate of the connecting springs).
What else is there to consider?-- Twizz, Sep 22 2011 I never said the mass doesn't experience jerk, or that different portions of it don't experience different jerks. Of course any time anyting changes acceleration, it experiences jerk. What I said was that the normal equations of motion completely describe said motion without a term for jerk, because jerk is not something unique or different, any more than velocity is fundamentally different from acceleration.
A perfect description of position adequately describes position, velocity, acceleration, jerk, and any higher derivatives you care to include. Terms in an equation only need to be added when something has an effect based on that term. Derivates up to accleration are routinely used because the effect of an applied force is best described in terms of acceleration.
Even if the mass is compressed and the force is traveling through it, each particle in the mass can still be described in terms of the forces acting on it and the resultant acceleration. There is no need to add a jerk term to get a complete equation of motion.-- MechE, Sep 22 2011 [Twizz], since each atom individually compresses a bit (see earlier annos talking about squashed electron clouds), and since that process takes time, it logically follows that each atom experiences jerk, and does not instantaneously reach the final acceleration value.
[MechE], what you have written is fine ONLY so long as there are NO events that are able to fall outside that simple no-term-for-jerk mathematical description. Yet one of the links in that "Drop and Stop Test" Idea ("Origin of the Equation") describes several things that appear to fall outside the simple description. Like cables breaking when the ordinary calcs concluded they were more than strong enough to handle the load....-- Vernon, Sep 22 2011 //if there were lots of places in Physics where the consequences of jerk couldn't be ignored, then Physics wouldn't have ignored it so much, right? So, if I happen to encounter a few worthy places, like the valves in an internal combustion engine, where jerk can be a significant factor, I see no reason to avoid mentioning it.//
Give a man a hammer, and suddenly everything's a nail.-- MaxwellBuchanan, Sep 22 2011 As we discussed in that idea, there is one of the few places were using jerk in your equations might make sense. Why? Because that's one of the easier ways to find the peak acceleration, which is the load the cables should be sized for. Regardless, what matters is the peak acceleration, not the jerk.-- MechE, Sep 22 2011 [MechE], perhaps "peak acceleration" is relevant, or perhaps jerk is relevant. That other Idea is all about putting it to the test....-- Vernon, Sep 23 2011 random, halfbakery