The Swing of a Pendulum

[Motor Daddy]

You haven't managed to discuss the detailed explanation I gave of the 2 rocket example, why should we move on to other things?

When you can tell me how you arrived at the acceleration rate of 10 m/s^2 then we can continue that discussion. Explain to me the technique you used to measure the acceleration rate of 10 m/s^2, because I know you have no knowledge of the absolute frame and the only way you can know an acceleration rate of 10 m/s^2 is to have measured it in the absolute frame against the light sphere. If you persist in your blind traveling ways we too can play the direction game and you will lose, as I previously showed that relative velocity is like a blind squirrel looking for a nut. Once in a while he'll find one (because even a blind squirrel finds a nut once in a while) by pure luck, but other than luck, it's a needle in a hay stack.

I know you have to resort to the 'Gish Gallop' tactic of throwing out as many ignorant claims and swamping peoples ability or desire to respond to them all but that doesn't make them automatically valid.

It may look like an ignorant claim to you because claims are relative, and you don't understand it.

You have not actually shown any contradiction in any kinematics, you have simply asserted things without justification.

I've shown that relative velocity is not the velocity that is changing under acceleration.

I said I'd discuss the torque question when you can actually properly formalise it. That's part of the problem talking with people like you, you cannot actually properly define a scenario, due to your lack of mathematical capabilities, and thus you always leave arm waving 'wiggle room' to ignore people who explain your mistakes.

The scenario speaks for itself. Do you have a question about the scenario? The math is there, check it, it's flawless!!

Just as the car/rocket example I formalised using basic kinematics can you do likewise with your torque example.

That is formalized. HP=Torque*RPM/5252. You know how to calculate the circumference of a tire I assume? You know what RPM is? You know what a gear ratio is? You know what mass, distance, time, force, work, power, acceleration, and velocity are I presume? Well get hot! Tell me why the car that has more HP at every MPH accelerates at a greater rate at every MPH! You have all the information in that example. We can go into the engine specifics if you like? Volumetric efficiency, bore, stroke, cam timing, duration, ICL, LSA...etc.. Just say the word

I said I'd discuss it with you if you could. You then saying "You're taking a long time!" is dishonest.

Why are you trying to dictate to me what is and what isn't a long time? I have a watch, and according to the watch, and my perception of the watch, you are taking a long time to answer the question I asked of you. There is nothing dishonest about that! You love to try to make claims of dishonesty, but you don't actually know the true meaning of the word. That's not to say that you're not dishonest, that's not what I mean. You certainly are!

And saying "I'm here to help" is laughable, since I've demonstrated I can formalise such scenarios while you're showing you cannot do it nor can you understand when others do it for you.

You don't seem to understand the meaning of the word help. I will help if possible. You laughing gives me the impression that you seem to think that you know everything and I could never in a million years teach you anything. That is total BS and you know it, since I'm pretty sure I could run circles around you in the physics of an internal combustion engine, just to give an example.

Until such time as you can formally construct the scenario pertaining to torque I do not see sufficient evidence that you understand it. Prove to me you understand it and can formalise that understanding and we'll talk. If you continue with this "You're taking a long time! Where's your response?" then I'll simply point you back to this post and report you for trolling. I'm asking you for a minimal level of understanding and honesty. I know you consider such things 'absolute nonsense' but that isn't my problem, it is yours.

That is formal. I gave you all the information you need. What information are you missing?

A car alone has no second object to be moving relative to but that doesn't matter. A single car which undergoes the acceleration described previously will still be able to measure that acceleration using accelerometers. It will then be able to say Initially I was in an inertial frame F. I underwent acceleration of magnitude a for time T. I am now in another inertial frame F'. The relative velocity difference between F' and F is therefore $$\Delta v = aT$$, F' is moving at speed v=aT compared to F. No need to know what, if any, absolute motion F and F' have. The car doesn't need a second object to compare itself with, it can do it all on its own since acceleration can be measured directly.

I can prove you wrong. What you are saying is that there is no absolute reality, and that is just flat out wrong. You are trying to say that it doesn't matter what the absolute velocity is, that all that matters is the acceleration of the two objects. I can draw two different scenarios of the relative velocity remaining the same, the acceleration of each rocket being the same, and with those numbers can make multiple realities. You are saying it doesn't matter which of those realities it is. Are you for real?? Math and physics is a tool used to describe reality, not reality describe physics and math!

If you ask the same question again, in a manner which is clearly meant to imply I haven't responded to the question when I have several times, then I'll start reporting you. I have no problem with people who don't know physics but want to understand it but someone who is wantonly ignorant and deliberately so I cannot abide.

Just because I don't agree with you doesn't make me ignorant. I asked you to walk through the scenario one step at a time so as to find the discrepancy between our methods and try to resolve the issue. You don't want to do that, maybe because you aren't capable of measuring reality and taking those measurements and using them in your theory to describe the reality that took place.

A ball of mass M is held in place at x=0 by a pair of massless springs (you can do it with just 1 but it doesn't matter) with spring constant k. (bad diagram but it looks like |\/\/\/\/\/\O/\/\/\/\/\/\|) The springs are not in tension (ie being compressed or stretched) when the ball is at x=0. This spring/mass system is inside a box inside a car. The car accelerates at rate $$a$$.

Based on what measurements?

The spring/ball system moves,

Does it move compared to the box or move compared to the light sphere, or both?

causing the left hand spring to be compressed and the right hand to stretch, |\/\/\/\/\O/\/\/\/\/\/\/\|. . The system moves to an new stationary equilibrium, with the ball at x=-L.

You're measuring the ball's position compared to the box. What is the box's position measured against?

Since the system is accelerating at rate a

How do you know the acceleration rate?

the ball must be and so it is experiencing a force F = Ma.

You better quit while you're ahead and stop talking about force. You first need to understand the torque/HP example before you know what force is.

The springs therefore must be applying this force. The spring which has been squashed by an amount L will push back with a force +kL. Likewise the stretched spring will pull back with a force +kL. Therefore the ball is experiencing a force F=+2kL.

If you want to measure force in that system that is fine, but those forces do not translate to the absolute frame, so all your "relative force" nonsense is just that, nonsense.

So we have Ma = 2kL, so a = 2kL/M = (2k/M)L. So if we know the strength of the springs, the mass of the ball and the distance it has moved we can compute the acceleration it experienced.

You only know the distance the ball moved compared to the box. You have no way of knowing what distance the ball moved in the absolute frame, which is according to the light sphere, which defines distance!

Nowhere have I had to say what the initial or final velocity of the car is. It could have started from stationary, with respect to the road, moving at 100kph or reversing a 54kph, anything. The acceleration measurement only requires me to measure the displacement of the spring mounted ball.

You still have not measured acceleration, you have simply created a new relative velocity. YOU DO NOT KNOW HOW FAR IN THE ABSOLUTE FRAME ANY OF THE OBJECTS TRAVELED!!!

I know I keep saying it but it really is true, this stuff is covered by children. I remember doing this when I was 14 or 15! Balls on springs or pendulums swinging is the stuff of basic physics lessons!

I need to go back to basics with your mentality because your theory makes unbelievable simple mistakes that any average person can comprehend. Create all the baffling BS you want and make it complex as you want, the mistake you make is simple and all the complexity is not going to change that!!!

As I just explained, the measurement of the acceleration really is very straight forward. The fact you didn't know this and also couldn't think up a way of doing it shows how narrow and flimsy your grasp of such things is. Must be somewhat depressing to have such a narrow view of things, struggling to grasp what children take for granted.

You have explained nothing except your method of deception. Crystal clear now! Tell me how you arrived at the 10 m/s^2 acceleration rate!!!

 

[AlphaNumeric]

I'm going to skip over most of your incoherent assertions and nonsense and focus in on the bits related to the spring/mass accelerometer. I don't want to give you a chance to skip over it.

When you can tell me how you arrived at the acceleration rate of 10 m/s^2 then we can continue that discussion. Explain to me the technique you used to measure the acceleration rate of 10 m/s^2, because I know you have no knowledge of the absolute frame and the only way you can know an acceleration rate of 10 m/s^2 is to have measured it in the absolute frame against the light sphere.

An assertion disproven by the two examples of accelerometers I have given you. The measuring of the deflection of the spring/mass system or the angle of the pendulum would give the acceleration experienced without having to consider anything else.

Based on what measurements?

The acceleration of the car can be measured using knowledge of its location at various times or it can be measured directly using accelerometers of the types I described.

Does it move compared to the box or move compared to the light sphere, or both?

This is only serving to show you don't understand the scenario I went through, else you'd not be asking such questions. It also demonstrates you cannot do such simple kinematics modelling because otherwise you'd be able to model it yourself and see for yourself. As I clearly stated in the post, the mass is deflected from the central position and it is the size of this deflection which is a measure of the acceleration experienced.

You're measuring the ball's position compared to the box. What is the box's position measured against?

Doesn't matter. All that matters is the deflection of the ball inside the box. The deflection is with respect to the walls of the box. Again, since you struggle to grasp thought experiments like this I'll give a more specific description.

A box is 1 metre in length. Inside 2 springs with spring constants k = 100g/s^2, are attached to the interior walls, one at the front and one at the back. They are of length 49cm each. Between them a spherical mass, of mass 100g and radius 1cm, is placed and joined to the springs. The centre of the sphere is therefore 50cm from each wall. The camera is put into the box and points at the sphere, at right angles to the springs. The camera is oriented in such a way that the distances the centre of the ball is from the walls can be measured (the interior wall has length markings engraved into it). This box is then put on a rocket in space and the rocket goes off and flies around doing whatever it does. The video of the ball during the journey is then processed, where a single frame from some point in the journey is shown to a person. The person is told the value of k and the mass of the ball. Can the person, with only a single picture from the video and the values of k and m, compute the acceleration the rocket was experiencing at that moment?

The answer is yes. Suppose the picture shows the deflection of the ball was 3cm, ie it was 47cm from one wall and 53cm from another. We know the value of k and by the formula I gave previously we have $$a = \frac{2k}{M}L = \frac{2*100}{100}3 = 6 cm/s^{2}$$. No information about the position or velocity of the rocket is needed. No need to make reference to an absolute position, all that matters is the position of the mass with respect to the walls, as that tells you the compression or stretching of the springs and thus the forces they are exerting. Simple.

You better while you're ahead and stop talking about force. You first need to understand the torque/HP example before you know what force is.

Actually torque is a concept which requires first an understanding of force, since it is the application of force displaced from a point of rotation.

If you want to measure force in that system that is fine, but those forces do not translate to the absolute frame, so all you "relative force" nonsense is just that, nonsense.

In other words since I got a working model which doesn't agree with yours it is wrong. I also didn't say 'relative force'. Acceleration and forces are not relative. Again, you don't know what the physics actually says!

You only know the distance the ball moved compared to the box. You. have no way of knowing what distance the ball moved in the absolute frame, which is according to the light sphere, which defines distance!

Yes, I only know the distance the ball moved compared to the box and yet I was able to measure the acceleration! It doesn't matter more information is needed for your take on things, in Newtonian and relativistic kinematic models no more information is required.

You still have not measured acceleration, you have simply created a new relative velocity. YOU DO NOT KNOW HOW FAR IN THE ABSOLUTE FRAME ANY OF THE OBJECTS TRAVELED!!!

And yet the acceleration can be computed without that information. I told you, these devices are real, they are used in gyroscopic systems for vehicles like cars and planes. You could build one yourself. Once you know the physical make up of the springs and the ball (ie mass and spring constants) you can work out the acceleration the box is experiencing even if you were locked inside the box with no knowledge of the outside world, as all you need to know is the change in position of the ball relative to the walls. The reason it is relative to the walls as what we're interested in is the forces the springs apply and that depends on how compressed or stretched they are.

Seriously, get some springs, a small ball and some glue. You can make the device yourself!

I need to go back to basics with your mentality because your theory makes unbelievable simply mistakes that any average person can comprehend. Create all the baffling BS you want and make it complex as you want, the mistake you make is simple and all the complexity is not going to change that!!!

You have failed to refute what I said, you have only managed to assert I don't have enough information, yet I can compute a value for the acceleration, as well its direction.

Try it for yourself. Build the mass/spring accelerometer and then put it on the ground such that the springs are aligned vertically. Obviously the bottom spring will compress and the top spring stretch, due to gravity. If you know the spring constant and the mass of the ball you can measure the displacement and get an estimate for the gravitational acceleration on the Earth's surface. There'll be an error due to the fact springs are not really massless but the method is sound.

And I like how you call this 'baffling BS'. If you consider stuff taught to 15 year olds 'baffling' you have serious problems with your science knowledge.

You have explained nothing except your method of deception. Crystal clear now! Tell me how you arrived at the 10 m/s^2 acceleration rate!!!

Consider yourself reported for trolling, since that has been addressed already. Simply ignoring when people give lengthy explanations, including how to build your own measuring device, you're doing nothing but trolling.

 

[Motor Daddy]

AN, I am going to draw a picture of a box with 2 springs and a ball. I am also going to include the light sphere in the pic, and I will also tell you the radius of the light sphere at every point in time. From that radius I can determine the center of the sphere. The center doesn't move, because the center of a light sphere is always at an absolute zero velocity. From that center point I am able to measure distance in the frame at every point in time according to the radius of the light sphere. You can not lie about changing absolute velocities, as everything in the presumably 3 dimensional (and time) pic represents reality. The reality the pic represents is absolute distance and absolute time. When you make up numbers what you don't realize is that you are not making up real absolute numbers, and unless you get lucky your numbers will not coincide with reality!

 

[AlphaNumeric]

The reality the pic represents is absolute distance and absolute time.

You claim it is how reality works but you have no evidence.

AN, I am going to draw a picture of a box with 2 springs and a ball. I am also going to include the light sphere in the pic, and I will also tell you the radius of the light sphere at every point in time. From that radius I can determine the center of the sphere. The center doesn't move, because the center of a light sphere is always at an absolute zero velocity.
....
When you make up numbers what you don't realize is that you are not making up real absolute numbers, and unless you get lucky your numbers will not coincide with reality!

You don't seem to be understanding the problem. Light spheres do not need to come into it when we're asking whether or not the spring/mass system can measure acceleration.

I describe the 'box with a camera' scenario in my previous post. Do you accept that if the mass of the ball and the spring constants are known then it is possible to compute acceleration the box experiences without having to know anything beyond the deflection of the mass?

Let's simplify it further, rather than you muddying the waters and considering a different scenario. Suppose the box is actually the back of a van. The van has no windows, no ways for you to communicate with the outside world. The ball is on a frictionless rail, aligned with the centre of the van and is held in place by the two springs. You know the spring constants and you know the mass of the ball. I claim that you can compute the acceleration the van experiences by measuring the deflection the sphere experiences from the middle of the rail. Do you agree? If not, please explain why we cannot measure the acceleration.

I would also point out that when we do this (using little accelerometer versions) we accurately measure the change in velocity a vehicle experiences, which we can measure in a different way by considering motion relative to the ground. We can measure the acceleration of a van by looking at where it is on a road. The accelerometer indeed measures the observed accelerations, without having to know anything about velocities. This is a baseless assertion on my part, this is an experimentally demonstrated fact. Accelerometers are used in missiles and aeroplanes to help guide them. No need for an absolute frame or absolute motion, acceleration can be measured without them and indeed is used in real world applications.

The problems with your understanding go right down to the level of what an inertial frame is, a concept in Newtonian mechanics too. Trying to bring light spheres into it is just going to confuse you. Stick with springs and masses until you grasp them, then move onto more elaborate constructs.

 

[Motor Daddy]

AN, Since you claim a=10 m/s^2, can you tell me how much time elapsed during your measurements of distance?

 

[Motor Daddy]

You don't seem to be understanding the problem. Light spheres do not need to come into it when we're asking whether or not the spring/mass system can measure acceleration.

No, it's YOU who doesn't seem to understand, the light sphere ALWAYS has to be in it, because without the light sphere you have no unit of measure of distance. Do you not understand how to measure distance using light? Certainly you must know how, since the very definition of the unit of measure the meter states that it is the length of the path that light travels in a vacuum in 1/299792458 of a second! How else would you know distance and direction without a light sphere??? You live in a 3 dimensional space, do you not?

I describe the 'box with a camera' scenario in my previous post. Do you accept that if the mass of the ball and the spring constants are known then it is possible to compute acceleration the box experiences without having to know anything beyond the deflection of the mass?

The mass will indicate a change in the box's absolute velocity has occurred. It is trivial to talk about how far the mass moved compared to the box, as the acceleration is of the box, not the mass. The box changed absolute velocity.

Maybe you are trying to claim that the changing of the mass compared to the box is proportional to the change in distance of the box in space? How would you know that, since you have no way of knowing how far the box is traveling in space, since you don't have a handy dandy light sphere available to measure absolute velocity.

Let's simplify it further, rather than you muddying the waters and considering a different scenario. Suppose the box is actually the back of a van. The van has no windows, no ways for you to communicate with the outside world. The ball is on a frictionless rail, aligned with the centre of the van and is held in place by the two springs. You know the spring constants and you know the mass of the ball. I claim that you can compute the acceleration the van experiences by measuring the deflection the sphere experiences from the middle of the rail. Do you agree? If not, please explain why we cannot measure the acceleration.

The change in the relative velocity of the ball compared to the van is an indicator that the absolute velocity has changed, but you have no idea how far of a distance the van traveled in space during that change in velocity.

An indicator would be like an idiot light on the dash of a vehicle. It would only be on or off when the absolute velocity is changing or not. The indicator can not tell you how far the vehicle traveled during the acceleration.

The problems with your understanding go right down to the level of what an inertial frame is, a concept in Newtonian mechanics too. Trying to bring light spheres into it is just going to confuse you. Stick with springs and masses until you grasp them, then move onto more elaborate constructs.

I understand relative and absolute velocity and acceleration in the absolute frame, and you are trying to tell me to try to learn it your way???

 

[Read-Only]

Nah! This is afterall, On the Fringe, Alternative Theories, etc, and I doubt Sf has run out of bandwidth.

I'm finding this discussion very interesting, enlightening and educational - irrespective of who is right or wrong.

And frankly, sceaming 'lock this thread', etc, kinda reminds me of the Emperors courtesans trying to silence the little boy ..

I'm not "screaming", just suggesting. And if you think Motor Daddy has anything here that interesting, you are just as ignorant as he is. He doesn't understand even the most basic things about physics taught to school children and neither does he understand how to use simple math - he just ignores it every time it's mentioned.

All you've accomplished in this thread is showing that your education - if you had one - has failed you also.

 

[AlphaNumeric]

AN, Since you claim a=10 m/s^2, can you tell me how much time elapsed during your measurements of distance?

Please tell me which post you're referring to so that I can give the appropriate elaboration.

No, it's YOU who doesn't seem to understand, the light sphere ALWAYS has to be in it, because without the light sphere you have no unit of measure of distance. Do you not understand how to measure distance using light? Certainly you must know how, since the very definition of the unit of measure the meter states that it is the length of the path that light travels in a vacuum in 1/299792458 of a second! How else would you know distance and direction without a light sphere??? You live in a 3 dimensional space, do you not?

The method by which the deflection of the mass from the central position is measured is immaterial. The fact is a closed box containing you and the spring/mass system is sufficient for you to work out whether you are accelerating and by how much. You said more information was needed, that a measure of velocity of the box was needed, that I needed to know the position of the mass compared to something more absolute, and I illustrated that not to be the case.

The mass will indicate a change in the box's absolute velocity has occurred. It is trivial to talk about how far the mass moved compared to the box, as the acceleration is of the box, not the mass. The box changed absolute velocity.

Once the mass has been deflected from its central position, say from the 50cm-50cm position to 47cm-53cm example I did, the mass no longer moves relative to the box, it is in an equilibrium condition. Therefore we know the velocity of the box and the velocity of the mass are the same. Since this was also true before the acceleration commenced we can say something about the box and the mass.

Maybe you are trying to claim that the changing of the mass compared to the box is proportional to the change in distance of the box in space?

No, I didn't say that. I said and then demonstrated using mathematics that the size of the deflection is proportional to the acceleration experienced. Zero acceleration means no deflection but a constant velocity, in some frame, would increase distance moved by the box.

I'm going to ask you a direct question, please answer it. Do you understand the mathematics I've posted? Do you understand how to do Newtonian kinematics involving constant acceleration, as described here? I suspect the answer is no, else you'd not have ask

How would you know that, since you have no way of knowing how far the box is traveling in space, since you don't have a handy dandy light sphere available to measure absolute velocity.

I explained this! That was the whole point of the post! The deflection of the mass from the centre is proportional to the acceleration. Where the box is and how fast it was moving is irrelevant, so we can work in any inertial frame we desire and still get the same result. This is a Newtonian example but the relativistic one is similar but more mathematically elaborate (and I think you're struggling enough with the Newtonian case).

The change in the relative velocity of the ball compared to the van is an indicator that the absolute velocity has changed, but you have no idea how far of a distance the van traveled in space during that change in velocity.

So what? If I'm trying to measure the acceleration I can do it without knowing anything about velocity.

The indicator can not tell you how far the vehicle traveled during the acceleration.

Doesn't matter, isn't needed.

I understand relative and absolute velocity and acceleration in the absolute frame, and you are trying to tell me to try to learn it your way???

I'll ask you again, are you able to do the mathematics here? If so then why do you ask the questions about what I was getting at, as you should be able to model such systems from the mainstream point of view yourself? If you don't then don't you think you're not sufficiently competent at basic kinematics in the mainstream to be able to properly critique it?

 

[Motor Daddy]

Enough!

Do you still claim the box accelerated at a rate of 10 m/s^2?

 

[AlphaNumeric]

Do you still claim the box accelerated at a rate of 10 m/s^2?

Did you even read my post? The first thing I said was to ask you to point to the specific post in question so we can talk about it properly. I am unsure which post you're referring to as I've talked about such a thing in a number of cases.

And I asked you a direct question, please answer it.

/edit

Are you referring to this one?

 

[Motor Daddy]

Did you even read my post? The first thing I said was to ask you to point to the specific post in question so we can talk about it properly. I am unsure which post you're referring to as I've talked about such a thing in a number of cases.

And I asked you a direct question, please answer it.

Do you have amnesia or something? I've been asking you how you determined that the acceleration rate was 10 m/s^2 for a couple pages now.

You are in a box. You are the ball suspended in the center of the box. At t=0 you claim to be at the center of the box. At t=1 you are no longer at the center of the box. Why are you claiming that the box changed motion when you have no idea if it was really you that changed motion??

 

[AlphaNumeric]

I'll assume you're talking about this one. Since it is a conceptual scenario I can define a few things (how else would we talk about it if I didn't describe the scenario?), one of which is the acceleration.

However, we can consider how we would know the magnitude of the acceleration in a real world system. In such a case we use the spring/mass system I described earlier. Someone sitting in the back of a van, without windows, using such a box would be able to compute the acceleration a vehicle undergoes by measuring the mass deflection. He can then compare his measurements with the driver who can say what the velocity change was by comparing the van's motion to the road.

The driver measures his speed relative to the road by the rate the wheels turn. This means he can trivially compute the change in velocity due to putting his foot down by looking at the speed meter on his dashboard before and after. The person in the back of the van will use the spring/mass system and he will be able to work out the change in velocity accurately, despite not knowing what speed he started or finished with.

Please answer this direct question : Do you think this is possible? Do you think the person in the back of the van can, knowing only the mass of the ball, the spring constant and the deflection of the ball's position, compute the acceleration the driver will measure? If not, why not?

 

[AlphaNumeric]

You are in a box. You are the ball suspended in the center of the box. At t=0 you claim to be at the center of the box. At t=1 you are no longer at the center of the box. Why are you claiming that the box changed motion when you have no idea if it was really you that changed motion??

The sphere will definitely move because it has a force applied to it due to the springs. For a moment of time when the box first accelerates the sphere will not move, due to inertia but then the forces caused by the springs being compressed or stretched will cause the sphere to accelerate. The spring/mass is only able to stay in the deflected configuration if the acceleration continues, as the springs otherwise will impart a force onto the sphere and return it to the equilibrium configuration (in the middle).

The only forces on the sphere are those from the spring (we're ignoring gravity in this example). If the ball isn't in the middle then it experiences a non-zero force from the springs and it will accelerate. Therefore regardless of whether it is the box which initially moves or whether another force perturbs the ball initially once the ball is no longer in the middle of the box it experiences a force, accelerates and thus cannot have been at constant speed throughout.

I note that you continue not to answer my question. Why not? It is simple enough, do you understand the SUVAT equations?

If you ask again about the 10m/s^2 I'll report you for trolling because I have now explained how an accelerometer works and how we can measure acceleration without having to know any absolute velocity or any velocity at all for that matter. The system can only stay in the deflected state if the acceleration continues, when it stops the system moves back to the original configuration. The 10m/s^2 value was a particular numerical example, the general principle I've covered using algebra and describing the accelerometer.

 

[Aqueous Id]

The pendulum indicates a change in absolute velocity.

No, it does not. The pendulum indicates an applied force.

The pendulum is non-responsive to changes in relative velocity between the two cars caused by the other car's change in motion.

This sets up a logical fallacy. It's irrelevant what the other car is doing.

Since the pendulum indicates a change in velocity,

You mean an applied force.

and the relative velocity doesn't change,

Relative motion between the cars, you mean. Not relevant.

the pendulum is indicating a change in absolute velocity.

No, it's indicating the slope (dv/dt) on the curve v(t) at each time t that a measurement is taken, which is inherently relative. Further, the entire curve is relative to the initial velocity (zero) which is relative to an initial reference frame, such as the parking lot where they started. Further, earth's gravity influences the pendulum, in an amount relative to the altitude and vertical direction of the car (as while ascending a mountain road). It's all entirely relative.

 

[Motor Daddy]

I'll assume you're talking about this one. Since it is a conceptual scenario I can define a few things (how else would we talk about it if I didn't describe the scenario?), one of which is the acceleration.

You can't just start by saying a=10 m/s^2. That has to be based on some type of measurements that took place over a duration of time. Are you really that naive about light travel time?

However, we can consider how we would know the magnitude of the acceleration in a real world system. In such a case we use the spring/mass system I described earlier. Someone sitting in the back of a van, without windows, using such a box would be able to compute the acceleration a vehicle undergoes by measuring the mass deflection. He can then compare his measurements with the driver who can say what the velocity change was by comparing the van's motion to the road.
The driver measures his speed relative to the road by the rate the wheels turn. This means he can trivially compute the change in velocity due to putting his foot down by looking at the speed meter on his dashboard before and after. The person in the back of the van will use the spring/mass system and he will be able to work out the change in velocity accurately, despite not knowing what speed he started or finished with.

The driver is computing the relative velocity as measured according to the road. The person in the back of the van has no way of knowing what direction of travel the van is traveling down the road. The driver sees the acceleration as an increase in speed from 20 m/s-30 m/s over the duration of 1 second, which is an acceleration of 10 m/s^1 . The person in the back of the van has no way of knowing if the velocity is increasing or decreasing.

 

[Motor Daddy]

Please answer this direct question : Do you think this is possible? Do you think the person in the back of the van can, knowing only the mass of the ball, the spring constant and the deflection of the ball's position, compute the acceleration the driver will measure? If not, why not?

Again, the driver will base all his measurements on the road, which has an unknown absolute velocity. The driver can not know which direction of travel he is traveling in space, he can only know which direction he is traveling relative to the road. I know which direction the driver is traveling.

 

[Motor Daddy]

No, it does not. The pendulum indicates an applied force.

The pendulum is indicating an acceleration. You have no way of knowing if the velocity is increasing or decreasing.

 

[billvon]

I know which direction the driver is traveling.

How do you know that?

 

[Motor Daddy]

How do you know that?

Because the light sphere can tell if the acceleration is an increase in velocity or a decrease in velocity.

 

[Motor Daddy]

http://www.freeimagehosting.net/ukkwm

Do you see how the absolute velocity is increasing? Do you see how it is impossible for the absolute velocity to be decreasing in that pic?