General > General Technical Chat
Force multiplier
Nominal Animal:
"If there is no net force the vehicle will not move."
A net force will accelerate a vehicle, not "keep it moving". Completely ignoring Newton's first law of motion, and accusing others of not understanding physics, is utterly, religiously, strange.
:horse:
electrodacus:
--- Quote from: Nominal Animal on February 11, 2023, 05:42:54 am ---This is also why I strongly oppose incorrect modeling (picking a few random forces, and claiming they describe the system, when they clearly do not), and prefer to start at kinematics, which is much easier to understand, and harder to get wrong. Understanding is not achieved by convincing others; it is achieved by making testable hypotheses, applying ones understanding, and comparing the results to the real world observed results. Because of this, I find Popperian falsifiability a more valid approach to science than basic verifiability. It is also exactly why instead of posting a video, I posted the exact description/recipe/model of a vehicle anyone can build and reproduce the findings: no need to take my word for truth, here is how you can find out for yourself.
I know now I cannot help electrodacus understand, no matter how much effort I spend, but I do hope I've helped anyone else reading this thread to not be convinced by electrodacus' physically daft but linquistically clever writings. On the surface, it looks so reasonable; but if you examine the questions and answers, you can see the lack of logic, rationality, and any kind of scientific rigor: only the opposite, a religious stance on incorrect assertions that no proof will ever shake.
:horse:
--- End quote ---
Yes kinematics is easier to understand and harder to get wrong but it does not represent reality.
I did not picked random forces as you claim. There is a single force F1 that is the input to the system. You can not expect any movement if you do not apply any forces. F2 and all others are consequence of the applied F1 so I did not made up forces.
I appreciate you trying to make me and others understand how this works as that is the same thing I try to do.
But kinematics is just not the tool you can use to find how this device works.
No unpowered device will be able to move in the opposite direction of the only applied force without using energy storage.
When have you ever pushed something and thing pushed against you with more force than you applied ?
You claim (let me know if I'm wrong) that vehicle in case (a) can move without any wheel slip ? But my videos of the real machine shows wheel slip in all cases.
The reason you can justify that is because you are imagining a different setup from that in case (a).
What you imagine is a free wheel treadmill and the applied force between the ground and vehicle body (that will get you exactly what the kinematic model shows and no slip involved).
But the problem in case (a) specifically asks that applied force is provided by the powered treadmill so F1 is applied to input wheel (right) relative to ground and not relative to vehicle body.
While the result will look very similar with the kinematic model the mechanism involved is very different.
You and it seems most others prefer the simpler kinematic model as it will look to predict the same motion (it is close but not the same) but I think the reality of what happens while more complex (involving energy storage and stick slip hysteresis) is important.
The reason I try to explain this particular device (a) is because people (multiple) have made the claim that it represents the equivalent of the direct downwind faster than wind vehicle when it is in fact representing the direct upwind vehicle and that is because they confuse the input with output.
As for the direct downwind faster than wind, what chance will I have to explain that witch is even more complicated as it involves pressure differential energy storage.
But I can make multiple prediction witch if tested will show the prediction to be super accurate.
For example the claim is that such a vehicle can drive for unlimited amount of time above wind speed and I know that it will start to slow down as soon as it gets to peak speed since at that point pressure differential stored energy will be used up.
Nobody even bothered to take a video from the side on the treadmill model (the one with propeller) to see that acceleration rate drops and not increases as they predict from wrong (invented) equations.
Anything that can be predicted from this vehicle I can predict accurately and I have not seen any real world example of behaviour that is not predicted by my current understanding.
And it seems strange to me that reality (ultimate test of any theory) showing energy storage is ignored or blamed on my setup which is exactly the setup in diagram (a) so the model of interest. Same with the slip that is also seen in the video. The locked and dragged example is again ignored.
All this behaviours are explained fully by Newton's laws of motion. My mistake is probably to assume that everyone will be at the same level of understanding as Newton itself because so much time has passed and we tested his theories but human genetics has not changed at all since his time so the amount of people able to understand and not just memorize his discoveries is still very limited.
--- Quote from: Nominal Animal on February 11, 2023, 06:48:24 am ---"If there is no net force the vehicle will not move."
A net force will accelerate a vehicle, not "keep it moving". Completely ignoring Newton's first law of motion, and accusing others of not understanding physics, is utterly, religiously, strange.
--- End quote ---
A net force is needed for a stationary vehicle to accelerate so increase in vehicle kinetic energy. An ideal vehicle will then maintain that speed (kinetic energy) without any additional energy input.
A real world vehicle will experience friction meaning that in order to maintain speed (maintain the same kinetic energy) it requires constant input power that ends up as heat.
So if you start form not moving relative to a reference say earth/ground a force needs to be applied relative to earth/ground for the vehicle to move.
You by using kinematics just ignore forces but to get that result you get from kinematics (it is possible) the force will need to be applied to vehicle body relative to ground or to any of the wheels relative to body but it will not work that way if applied force is relative to ground to the wheel on treadmill.
So yes ignoring forces you can get whatever you want but is not the correct description of what happens when force is applied to wheel relative to ground.
Nominal Animal:
--- Quote from: electrodacus on February 11, 2023, 07:41:28 am ---I did not picked random forces as you claim.
--- End quote ---
You picked two out of all the ones in the system. How you picked them, I cannot say (and therefore used the term "random"), but they do not constitute any kind of model of the system.
--- Quote from: electrodacus on February 11, 2023, 07:41:28 am ---But kinematics is just not the tool you can use to find how this device works.
--- End quote ---
Yes, it is. It is telling that you cannot even understand how useful kinematics analysis is.
--- Quote from: electrodacus on February 11, 2023, 07:41:28 am ---No unpowered device will be able to move in the opposite direction of the only applied force without using energy storage.
--- End quote ---
That is utterly wrong. All you need is a suitable gearing.
The simplest example device is a spool of thread, rolling on its axis on two rails, with the radius of the spool larger than the wheels on the rails (and that is the reason you need the raised rails, as otherwise the spool would touch the ground), and the thread coming off the spool from the underside. When you pull on the thread, the spool rolls in the opposite direction.
The key is the gear ratio, just like in your vehicle. When the wheels are on the same axis, it suffices that the driven wheel is larger than the driving wheels. It is more obvious whenever the ratio of the wheels is large.
When you vary the spool-to-wheel ratio, at certain point you can make it switch directions. You can also switch directions by having the thread come off the spool from the top, which yields the same behaviour as negating and inverting the spool-to-wheel ratio, as shown by the kinematics math.
Do you want me to show you a diagram of its exact properties and Newtonian mechanics? Not just kinematics, but all the forces, assuming the device is made of uniform rigid material (say, 3D printed in PLA with 100% infill)? I can, but would it help? You probably would just invent some new forces or other inane reasons to not agree with physics and reality. So, I think it would still be more useful if you tested it yourself. After all, all you need is two rails and a spindle (an axis with a small wheel, then a spool, and then another small wheel), the wheels much smaller than the spool (say, diameter 1/4 of the sool diameter), and you can clearly observe and test its behaviour yourself. Heck, if you use a round stick as both the axle and the wheel, it's very simple to do!
In fact, a related device is often used as a physics experiment, with the unspooling thread replaced by gravity. The wheels form a double cone, bases against each other, apexes outward, and the rails are not horizontal or parallel, but converge downwards. The ratio of (half of) the rail angle and the conical angle corresponds exactly to the gearbox ratio here. At 1:1, the vehicle does not move. At larger than one ratios, the vehicle travels upwards along the diverging rails (because its center of gravity goes down, i.e. it converts potential energy to kinetic energy). At smaller than one ratios, the vehicle travels downwards along the converging rails (because its center of gravity goes down too). All this without any kind of initial push.
--- Quote from: electrodacus on February 11, 2023, 07:41:28 am ---When have you ever pushed something and thing pushed against you with more force than you applied ?
--- End quote ---
That is a false simile, and wrong.
--- Quote from: electrodacus on February 11, 2023, 07:41:28 am ---You claim (let me know if I'm wrong) that vehicle in case (a) can move without any wheel slip ? But my videos of the real machine shows wheel slip in all cases.
--- End quote ---
We are telling you your machine slips because its gear ratio is too close to 1:1, and it suffers from loss of traction. To fix, you only need to increase the gear ratio.
You refuse, because you axiomatically insist that the gear ratio is irrelevant. Even after even a simple kinematics analysis shows that the gear ratio is the key factor in describing the behaviour of these vehicles.
Why do you think that one incorrect example is proof that no solution exists? Even when everyone else is telling you how to correct your example so that it would show the solution you, and only you, claim is impossible?
When did you look at a broken car, and decide that because it didn't work, no four-wheeled car-like device could ever work?
cbutlera:
--- Quote from: electrodacus on February 11, 2023, 02:51:31 am ---
--- Quote from: cbutlera on February 11, 2023, 01:53:24 am ---
--- Quote from: electrodacus on February 10, 2023, 11:54:19 pm ---...
If not convinced by this think about a balance with fulcrum the third point offset as in image below.
Nothing will need to move for the input force to be smaller than output force and Newton's 3'rd law works here as two separate loops with F1 input force having a pair at the fulcrum and the other pair F2 output also relative to fulcrum.
But example a has no 3'rd point the fulcrum equivalent so with that missing input and output force can only be equal.
--- End quote ---
I can see that now. Your lever and fulcum example clarifies your understanding of Newton's third law to me quite well.
...
--- End quote ---
Can you clarify where your think understanding of Newton's third law differs from mine ?
...
--- End quote ---
In what you wrote above you described Newton’s third law working in loops involving more than two bodies.
“To every action, there is always opposed an equal reaction; or, the mutual actions of two bodies upon each other are always equal, and directed to contrary parts.”
The law explicitly applies and only applies to the “mutual actions of two bodies upon each other”, not three bodies in a loop, nor four bodies in a loop, nor any other number of bodies in a loop.
One of your most frequently stated claims in this thread has been that almost everyone who has commented here doesn’t understand Newton’s third law.
I wrote in detail about Newton’s third law in message #37 in this thread, and messages 39, 41, 43, 45, 49, 53, 56, 80, 82, 109, 118, 129, 133, 135, 137, 141, 184, and 188. Did you really manage to read all of those messages, and not spot the very difference in understanding that you claim to see between almost everyone else and yourself?
You tell us that you want to correct the misunderstanding that most of us have about Newton’s third law.
If you have identified my common misunderstanding then here is your chance, tell me where I am going wrong. And use the example on the Wikipedia page of the book resting on a table, which is a standard example used when teaching Newton’s third law. Don’t use an unnecessarily complicated example such as a trolley with a gearbox. It should be obvious by now to anyone except the most bone-headed, that using that example isn’t going to get the message across. If you can’t explain my misunderstanding using the book resting on the table as an example, then you don’t understand it yourself.
For a long time I have been giving you the benefit of the doubt, but I have reached my troll test moment in this thread. If you can make a credible attempt to explain why you think that I don’t understand Newton’s third law, using the book resting on a table as the example, then I will continue to participate. If you don't even try, then I too am out of here.
electrodacus:
--- Quote from: Nominal Animal on February 11, 2023, 09:19:39 am ---You picked two out of all the ones in the system. How you picked them, I cannot say (and therefore used the term "random"), but they do not constitute any kind of model of the system.
--- End quote ---
The "vehicle" has only two points of contact with the outside world and there is no internal power source (no motor or engine).
So all that is needed to know are the values of F1 and F2 since only those are relevant. F1 is the input due to treadmill and we need to know what the value of F2 is in relation to F1 to know of there "vehicle" can accelerate in one of this two directions.
--- Quote from: Nominal Animal on February 11, 2023, 09:19:39 am ---Yes, it is. It is telling that you cannot even understand how useful kinematics analysis is.
--- End quote ---
Kinematics has some uses but can not be used to predict how the "vehicle" will move in specific conditions like if it had an internal engine appling the force to one of the wheels relative to vehicle body (the part in blue) or if an external force between the ground and vehicle body was applied.
--- Quote from: Nominal Animal on February 11, 2023, 09:19:39 am ---
--- Quote from: electrodacus on February 11, 2023, 07:41:28 am ---No unpowered device will be able to move in the opposite direction of the only applied force without using energy storage.
--- End quote ---
That is utterly wrong. All you need is a suitable gearing.
The simplest example device is a spool of thread, rolling on its axis on two rails, with the radius of the spool larger than the wheels on the rails (and that is the reason you need the raised rails, as otherwise the spool would touch the ground), and the thread coming off the spool from the underside. When you pull on the thread, the spool rolls in the opposite direction.
The key is the gear ratio, just like in your vehicle. When the wheels are on the same axis, it suffices that the driven wheel is larger than the driving wheels. It is more obvious whenever the ratio of the wheels is large.
When you vary the spool-to-wheel ratio, at certain point you can make it switch directions. You can also switch directions by having the thread come off the spool from the top, which yields the same behaviour as negating and inverting the spool-to-wheel ratio, as shown by the kinematics math.
Do you want me to show you a diagram of its exact properties and Newtonian mechanics? Not just kinematics, but all the forces, assuming the device is made of uniform rigid material (say, 3D printed in PLA with 100% infill)? I can, but would it help? You probably would just invent some new forces or other inane reasons to not agree with physics and reality. So, I think it would still be more useful if you tested it yourself. After all, all you need is two rails and a spindle (an axis with a small wheel, then a spool, and then another small wheel), the wheels much smaller than the spool (say, diameter 1/4 of the sool diameter), and you can clearly observe and test its behaviour yourself. Heck, if you use a round stick as both the axle and the wheel, it's very simple to do!
In fact, a related device is often used as a physics experiment, with the unspooling thread replaced by gravity. The wheels form a double cone, bases against each other, apexes outward, and the rails are not horizontal or parallel, but converge downwards. The ratio of (half of) the rail angle and the conical angle corresponds exactly to the gearbox ratio here. At 1:1, the vehicle does not move. At larger than one ratios, the vehicle travels upwards along the diverging rails (because its center of gravity goes down, i.e. it converts potential energy to kinetic energy). At smaller than one ratios, the vehicle travels downwards along the converging rails (because its center of gravity goes down too). All this without any kind of initial push.
--- End quote ---
You think that because you do not understand that a gearbox requires 3 point of contact with the outside world in order to be able to do force multiplication.
Any device including your spool example that moves in the exact opposite direction of the applied force requires energy storage and a trigger mechanism like in this cases stick slip hysteresis.
All you need to apply the force to the thread slowly and you will see that you increase the force and spool will not move until a very sharp transition when spool starts to move even as you no longer apply any force but then due to friction the spool will slow down so you need to apply force again.
This sort of behaviour will not exist on a gearbox where input and output force will be continuous as there are no charge discharge cycles.
When you pull on the string the spool will be dragged towards you but it can not move due to static friction at the points where spool contacts the ground.
At some applied force the spool will slip and the elastic energy stored in the wire will make the spool rotate as there is less energy needed to make the spool rotate than to slide towards the applied force.
I will say that a slow motion video will clarify all the above mechanism but I think you will blame the setup and try to find ways to change that other that to acknowledge that energy storage and stick slip hysteresis are involved.
--- Quote from: Nominal Animal on February 11, 2023, 09:19:39 am ---
--- Quote from: electrodacus on February 11, 2023, 07:41:28 am ---When have you ever pushed something and thing pushed against you with more force than you applied ?
--- End quote ---
That is a false simile, and wrong.
--- Quote from: electrodacus on February 11, 2023, 07:41:28 am ---You claim (let me know if I'm wrong) that vehicle in case (a) can move without any wheel slip ? But my videos of the real machine shows wheel slip in all cases.
--- End quote ---
We are telling you your machine slips because its gear ratio is too close to 1:1, and it suffers from loss of traction. To fix, you only need to increase the gear ratio.
You refuse, because you axiomatically insist that the gear ratio is irrelevant. Even after even a simple kinematics analysis shows that the gear ratio is the key factor in describing the behaviour of these vehicles.
Why do you think that one incorrect example is proof that no solution exists? Even when everyone else is telling you how to correct your example so that it would show the solution you, and only you, claim is impossible?
When did you look at a broken car, and decide that because it didn't work, no four-wheeled car-like device could ever work?
--- End quote ---
I will not say that 2:1 is anywhere close to 1:1. I will understand if it was 1.1:1 but not 2:1
No matter the gear ratio one of the wheels will need to slip for the vehicle to move.
But I can give you an example that you can no longer contradict.
Build a 1:1 version and push on the body (apply a force between ground and the body) the vehicle will move exactly how the kinematic model will predict and there will be no slip.
Then take the exact same 1:1 version and pull the paper under one set of wheels (treadmill) and you will see that all you get is slip and no movement.
That will tell you definitively that kinematics can not be applied to predict the motion of the treadmill example as forces are involved and kinematics ignores forces.
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