This is a multi-part message in MIME format. ---------------------- multipart/alternative attachment Well, I exaggerated the situation for the sake of emphasis. Adding lead = weights to the keys and/or moving them will change its moment of = inertia. =20 Will it change very much? Will you be able to detect the difference? Well, that's why we have engineering units for m.o.i. (slug-ft^2, or = kg-m^2) and a way to calculate it...otherwise we'd be shooting in the = dark. And if we know the moment of inertia before and after we add/move = the leads, we can calculate a percent change to get a relative sense of = what's going on. That way we don't have to have a "feel" for how much a = killogram-meter-squared is. So, for example, if we calculate the m.o.i. with no weights and then = calculate it again after we've added weights and the difference is a 20% = increase, we can say that the mechanism is now 20% more sluggish, which = would be much more noticable than if it were 0.01% more sluggish. = Obviously, putting a quarter in the fat kid's pocket is less "noticable" = than putting a bowling ball in his lap. You'll just have to do the math and see. That's what engineering's all = about. The weights may be small and the key large, but the key is only = wood and uniform; the weights are lead and concentrated away from the = pivot point. You may find out that they are negligible, or you may find = that they have a profound effect. I'm guessing that they'll be = somewhere in between, but you won't know till you figure it out. Don A. Gilmore Mechanical Engineer Kansas City ----- Original Message -----=20 From: Ed Sutton=20 To: College and University Technicians 'Subject: Re: What does the moi = feel like? Yes! And isn't this "sluggishness" the "MOI" we've been talking = about???? I know the image of the kids on the teeter-totter. In fact, I've = often used the image of elephants on the teeter-totter! And I suppose in a blindfold test, I could tell by pushing if the = teeter-totter was empty, or had the elephants in place. But here we have been discussing the merits of placing two leads at = the front of the key, or four at the back. In principle this makes = plenty sense, but in practice , we aren't dealing with anything like the = degree of difference between the empty teeter-totter and the one with = the kids or elephants. We are dealing with very slight differences of = key lead placement in piano actions, where most of the "sluggishness" we = feel comes from the hammers. "Sluggishness" is a powerful sounding word, but in a situation close = to the zero friction, zero gravity experiment, do you think you could = distinguish between the key with two leads at the front and the key with = four at the back (located to produce identical frontweights) by pressing = the key with your finger to produce different hammer velocities? Ed Sutton ----- Original Message -----=20 From: Don A. Gilmore=20 To: College and University Technicians=20 Sent: Monday, January 05, 2004 9:42 PM Subject: Re: What does the moi feel like? Hi Ed: All that would be left is the "sluggishness" of the parts, i.e. the = tendency of the key not to want to move and not to want to stop moving. = The force required would be proportional to how quickly you try to = change the speed of the key. Incidentally, if you totally balance out = the weight of the hammer, the key won't come back up to its starting = position. Think about an ordinary playground teeter-totter. With no one in = either seat, it is easy to move it around and it stays where you put it. = Now put a fat kid on either end (both the same weight). It's still = balanced and stays where you put it, but it is much more difficult to = start and stop it. The fatter the kids, the more moment of inertia the = system has. To start one kid upward quickly takes a big heave. Then if = you want to stop him it is also difficult; in fact, he may actually lift = you off the ground if he has enough energy at that point. The feel = would not be the same at all for an empty teeter-totter. Note that since the system is balanced, any disturbing force can tip = the teeter-totter, no matter how small (neglecting friction). I can = drop a small brick in one kids lap and start the lever turning and it = will accelerate faster and faster until he strikes the ground. The key = concept to realize is that the teeter-totter will accelerate at a = greater rate if I drop the same brick onto it when it's empty than with = two fat kids sitting in it. If I put two 500-lb. slabs of concrete in = each seat, the brick will accelerate them even less, though the system = is still balanced.=20 Don A. Gilmore Mechanical Engineer Kansas City ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/caut.php/attachments/57/75/b2/14/attachment.htm ---------------------- multipart/alternative attachment--
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