On Thu, 24 Jan 2002 20:15:11 John Delacour wrote: > >Now that really is playing with semantics :-) > Turnabout is fair play. :-) >> > If I press on the unloaded soundboard (no strings) it is >> > clear that every molecule of this column will move downwards at >> > exactly the same speed... >> >>This doesn't seem consistent with your stack of magnets analogy to >>me. Even in an unloaded board, the bridge has stiffness and the >>board has stiffness, so you're offering some resistance to the >>bottom magnet.... > >No, I said press on the _soundboard_, not press on the top of the bridge. OK >>And what does the output from the accelerometers mean? Does it indicate >>that those points are physically moving? I thought this idea was scoffed at >>before? > >Not at all. When a particle or a tiny part of the medium is first >set in movement (oscillation) it will be moving with reference the >remainder of the medium which remains undisturbed until other >particles are affected in the passage of time. The particles of the >medium in equilibrium (neglecting their constant vibration due to >heat, which is not a factor) are in a fixed relation to each other. >If a force is applied to the medium in one direction and meets no >opposition, this relation will not change. If pressure is applied at >the top and an irresistible force opposes it at the bottom, there >will be a change in this relation and compression. If a periodic >force is applied at the top opposed to a firm resistive (but not >irresistible) force at the bottom, there will be vibration and >localized differential movement of particles within and at the >surfaces of the medium, which I distinguish from bodily movement. > >JD > What I was asking is whether the point that the accelerometer is attached to has to be moving for the accelerometer to have a reading? If the accelerometer is attached to the top of the bridge and the accelerometer is showing a reading then that point at the top of the bridge must be moving, regardless of what is happening to the molecules underneath it in the bridge or soundboard. If that point was sitting fixed in space with the molecules beneath it doing whatever they are doing then the accelerometer would show no reading. Do you agree with this? Phil F
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