General > General Technical Chat

Newton's third law problem.

<< < (14/55) > >>

james_s:

--- Quote from: IanB on November 22, 2022, 09:06:16 pm ---There's really no point.

You know that thing children do, when they are playing a game and about to lose, they find some way of cheating so they can try to avoid the outcome? Electrodacus is playing that game here. There is no evidence you can provide, no experiment anyone can perform that will persuade him, because he will just come up with some kind of nonsensical word salad to dispute the result.

Notice how he never does any analysis himself, never shows any equations, but always tries to make other people do the work? It's a game for him, trying to make people jump to his command, and then getting satisfaction from the "power" that gives him. As I said above, this has all the signs of sociopathic behavior. It is really best not to enable it.

--- End quote ---

Just put him on your ignore list, one less source of noise.

IanB:

--- Quote from: Nominal Animal on November 22, 2022, 11:06:14 pm ---If I were still believing I might be able to help electrodacus see, I would have added another figure that contains the force vectors.  The key vectors would obviously be the two torques around the gear axis, because once one realizes their importance on how this system works, everything else including friction/stiction/traction becomes obvious and straightforward.  But no, I haven't drawn such an image, and will not.  Anyone truly interested in the subject can use any (classical) mechanics 101 book, and draw this themselves, and work it all out.  Or indeed grab some Technic Lego, and build working models, and compare their behaviour to what I described.

--- End quote ---

The interesting and important thing about the analysis of kinematic structures, is that forces or force vectors are not required in the analysis, in fact trying to use forces just makes the system harder to understand.

You have a system of rigid elements connected at various points by pivots or hinges, or in the case of wheels or gears the contact points. Since all the elements are rigid, there are equations involving only (x, y) coordinates that relate all the points in the system. All you have to do is to move one point, and all the other points will move in unison as governed by the connections. It is a pure problem of spatial geometry, with no force, energy, power or momentum involved in the analysis. (For example, consider a pantograph.)

electrodacus:

--- Quote from: IanB on November 22, 2022, 11:20:39 pm --- It is a pure problem of spatial geometry, with no force, energy, power or momentum involved in the analysis.

--- End quote ---

That is your problem. It is not just about geometry.
With that even 1:1 gear will work fine.
A 1:1 will not work even in theory and close to 1:1 will not work in practice due to losses.  The higher gear ratios work due to energy storage but you can not know that if all you look is geometry. 

PlainName:
Why is this started up again, electrodacus? No-one can change your mind, and you can't change the laws of physics or the opinions of anyone not you. That's been amply demonstrated in more than one lengthy thread previously.

So... why did you start this again? The only reason I could think of if someone else had done so is because they still couldn't solve the problem and wanted some help to clear up some points. But you don't - you know what you know and nothing is going to change that. Even if there was something you were unsure of, you wouldn't accept what anyone explained or demonstrated anyway unless it fit your already decided solution.

Nominal Animal:

--- Quote from: IanB on November 22, 2022, 11:20:39 pm ---
--- Quote from: Nominal Animal on November 22, 2022, 11:06:14 pm ---If I were still believing I might be able to help electrodacus see, I would have added another figure that contains the force vectors.  The key vectors would obviously be the two torques around the gear axis, because once one realizes their importance on how this system works, everything else including friction/stiction/traction becomes obvious and straightforward.  But no, I haven't drawn such an image, and will not.  Anyone truly interested in the subject can use any (classical) mechanics 101 book, and draw this themselves, and work it all out.  Or indeed grab some Technic Lego, and build working models, and compare their behaviour to what I described.

--- End quote ---
The interesting and important thing about the analysis of kinematic structures, is that forces or force vectors are not required in the analysis, in fact trying to use forces just makes the system harder to understand.
--- End quote ---
I know and agree.  If you look at my posts in this thread, I've said so myself, and instead described the system behaviour in terms of surface velocities or displacements in the math snippets.

If we had managed to progress to the "okay, I now see how this behaves so; but when and how does the slippage I saw occur? And why didn't my original approach describe the system?" stage, then we could have moved on to the forces.  Not to describe the behaviour of the system, but to describe why any simplified force-based description fails.  It is a pedagogical pattern that has often worked well: you look at the situation from a completely different approach, and only if/when you finally grasp the behaviour, you close the loop by examining how and why the original approach failed.

Here, you would only care about the forces if you wanted to find out the limits where slippage occurs; the coefficients of friction and system weight that are required for no-slip operation at a given gear ratio.  Starting from that is silly.

Where the insistence of energy storage being involved here stems from, I can only imagine.  There is no need for one.  The same math is valid both at standstill and at any velocity, continuously.  Even if one were to examine the forces, one would see they balance perfectly at each instance; with the only "energy storage" being the linear and angular momentum in the "car" or "spool", both perfectly aligned in the direction of travel.  No vertical motion at all, unless slippage occurs; and the systems I've described are explicitly in the no-slip cases.  You can make all sorts of things "work" if they slip a bit, but these ones do not need slippage or energy storage to behave as I've described.

:-//

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod