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  • #16
    Originally posted by andywander View Post
    The exact ratio doesn't matter. Just that there is a longer lever when you are using a ring.
    And longer lever enters into the equation as the squared force it takes to accelerate it from point A to point B, and that acceleration rate is double that of base middle VS edge... regardless of base size, as base size is always double of base center point,,, so again as far as quick acting dynamics the ring wins out .
    Last edited by A.K. Boomer; 12-23-2020, 08:43 PM.

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    • #17
      The moment of inertia of the ring about the vertical axis is far greater than a glob at the axis. The ring is more stable.

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      • #18
        Originally posted by SVS View Post

        Draw a diagram with weight at a point times distance from edge. Sum these “moments”. Blob at center will turn out equal to ring. (statically)

        I think AK is saying ring will have more rotational inertia (flywheel effect) and I can’t disagree.

        Was not talking that effect - but now that you bring it up, if the base starts to rotate due to uneven mass attached as it's tipping then the ring really wins out on stability --- you could not have brought up a better example of why it's so important for high performance cars to have light wheels in testing 0-60 times but even more importantly light tires as they are on the outer most parameter and count the most....

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        • #19
          The ring-shaped weight is more stable, because it has a higher moment of inertia with respect to the rotational axis associated with tipping.

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          • #20
            Originally posted by tomato coupe View Post
            The ring-shaped weight is more stable, because it has a higher moment of inertia with respect to the rotational axis associated with tipping.
            In as few of words as possible - this is put very direct and well said...

            I do have to even edit this though and go back to my original statement of "vibration" or bumps of the object VS static holding strength, two totally different things and in fact with something like "tipping angle" the ring is no more stable then the center weight, but as soon as you introduce dynamics everything changes...
            Last edited by A.K. Boomer; 12-23-2020, 09:18 PM.

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            • #21
              Originally posted by andywander View Post
              Well, i disagree with the most of youse guys.

              I think the ring will be more stable.

              Look at it this way-to tilt the stand you need to lift the weight that is on the side that you are tilting the stand way from.

              1/2 lb on an 8" lever arm will be a lot harder to lift than 1/2 lb on a 2" lever arm.

              Or take it to an extreme-distribute the weight around a 20' diameter. I think it will be a lot more stable.
              Except that it's not a 1/2lb in the case of the ring. Or rather that the ring might be a half lb but you're not tipping the whole half pound up at the far side away from the fulcrum. The ring's weight distributed around the base so only part of it is out on the other side being lifted and part is up close to the fulcrum and the rest is in between so has an effect based on the distance away from the fulcrum. And if you add up all that it it comes down to the center of gravity of the ring being what counts. And ring or blob either way with the center of mass being in the middle of the stand the leverage will be the same.

              The height of the blob was mentioned. And yes, while minor if the block was a tall cylinder than it would be less effective than the same weight as a low height flat ring. But if the "blob" is a disc of weight the same thickness as the ring then the two weights would have the same effect on the stability.

              Edited to add- as to the dynamics and inertial moments? Yes, it would take a more energetic short term blow to the stand to make the ring version tip over.

              But for static stability as in how far one could lean the stand over and have it fall back to upright either option is the same.
              Last edited by BCRider; 12-23-2020, 09:32 PM.
              Chilliwack BC, Canada

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              • #22
                Now lets see! I surmise that you are making a stand for a pedestal grinder and you want to know if you should put the post in the center of the truck brake disc or to off set it. I vote to set it forward. How far off am I?

                Sarge41

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                • #23
                  Yes, it is the center of gravity, aka, the center of mass that determines the stability. The center of mass of a ring around the outer edge vs. a blob at the center will both be at the center as long as the ring is symmetrical. As eKretz stated in post #4, the ring would have a slight advantage because it would probably have a lower center of mass than the blob. But that is the only difference and as he said, it will probably not matter until the stand is almost completely horizontal anyway.

                  As for those who argue about lever arms, I suggest you take an integral calculus class and learn how to do the calculation. When the infinite number of lever arms, each with their own infinitesimal mass (part of the ring or blob) are calculated and summed, you will see that the two are the same as long as the heights of the centers of mass of the two shapes are the same and both are symmetrical about the center.

                  This is a static analysis, not a dynamic one.



                  Originally posted by SVS View Post
                  Where is the center of gravity in the two cases?
                  Paul A.
                  SE Texas

                  And if you look REAL close at an analog signal,
                  You will find that it has discrete steps.

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                  • #24
                    Originally posted by Paul Alciatore View Post
                    This is a static analysis, not a dynamic one.
                    Yes and no. In a purely theoretical, which will tip first if I slowly lean this stand over til it falls, you are exactly correct. But for a mic stand subject to bumps that may tip it over, a greater mass moment of inertia will be considerably more stable. The real world is unfortunately not very static. Therefore I agree with rickyb, a ring would be the most helpful in this case.

                    Originally posted by rickyb View Post
                    The moment of inertia of the ring about the vertical axis is far greater than a glob at the axis. The ring is more stable.
                    21" Royersford Excelsior CamelBack Drillpress Restoration
                    1943 Sidney 16x54 Lathe Restoration

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                    • #25
                      I think the center of gravity is the same in either case- the ring wins over the blob in rotational inertia- and in tipping inertia too.

                      If this was a stand for a pedestal grinder, I'd offset the weight towards the front as well. But no, this would be for a mic stand, and potentially a rock legend is going to uproot it and swing it around while yelling into it. The inertial effects would come into play, but to what degree I don't know.

                      I think an experiment is in order. A thin, round, lightweight plate is fitted with a vertical, which has a hook on the top. Some large nuts are gathered and spaced out around the rim, and a spring is fitted to the hook. Pulling the spring to one side tips the plate up at one edge. Then all the weights are pushed towards the center of the plate and the spring pulled again. The extension of the spring shows the force required. Will these be two different numbers?
                      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                      • #26
                        Originally posted by Paul Alciatore View Post

                        I suggest you take an integral calculus class and learn how to do the calculation. When the infinite number of lever arms, each with their own infinitesimal mass (part of the ring or blob) are calculated
                        Yeah... Well.. Fuk that is my first response.

                        I or no one else likes suggestions from someone unless they specifically asked for a sugg? Did they?

                        Well then keep that chit in yer pockets until time to say Hey! Guess what I know today!!

                        JR

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                        • #27
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                          • #28
                            The blob would have a higher centre of gravity than the ring, so the ring would be very slightly better.


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                            Last edited by old mart; 12-24-2020, 11:29 AM.

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                            • #29
                              Originally posted by tomato coupe View Post
                              The ring-shaped weight is more stable, because it has a higher moment of inertia with respect to the rotational axis associated with tipping.
                              Couldn’t have said it better myself.

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