SuperSlim

And that's what I observed. The water in the bowl returned to its 'non-excited' state when I stopped rubbing the edge.

One, maybe last, observation. Because of the one-dimensional gravity field, determined by the local g, the rubber sheet model demonstrates curvature in an orbital plane. But an observer of curved geodesics for light rays can posit a 2d slice anywhere; the choice is arbitrary but determined by the direction of gravity in the experiments.

I personally think you need to look at the analogy in terms of a schematic view; the sort of thing a lecturer might use to demonstrate a 1st order 'solution' for an elastic surface curved by matter. Since, in my further opinion the videos from NZ successfully demonstrate several aspects of the Newtonian model, I congratulate the faculty for the eye-opener: spacetime is an elastic medium, distorted by the presence of massive objects. Since you can represent a lot of Newtonian orbital dynamics (modulo the friction), the elastic sheet is just the thing to let local gravity demonstrate an elastic force in action. Notice in the videos the initial vertical oscillations die out, the sheet is then in equilibrium so mg = kx for the background. The experiments in the videos are using Newtonian mechanics in a clever way, to show there's a good heuristic in there, somewhere. The bending of light rays from distant objects around the deformations, shows that the heuristic of a two dimensional sheet of distorted spacetime works for rays of light in two dimensions. We know this is true independently of coordinates, so it's just one sheet but there's a lot more of them. The UOW videos are serious science, except with a constant g everywhere where you only need one sheet, so why not use one with the right k, and stretch it as uniformly as practical to give it the same tension everywhere? I personally would like to see measurements of sound profiles, when striking the sheet with and without a massive object in the middle: what does the tonal response say about the tension, i.e. how well tuned is it? I just realised another problem with the analogy, the physical model is a catenary 'minimal surface' in a gravitational field; initially it looks like it's loosely tensioned, the problem is fixed by assuming it's actually flat, the bending in the sheet is because it has mass, you need to factor this out of the model to get a spacelike sheet.

Ok thanks. What I'm actually trying to figure out is why a torque wrench has a graduated scale that measures this angle, in mass x distance units. Do I start with forces, or is it a derivative of the momentum? I realise that the time interval in the bending isn't in the result because it's time-independent and depends only on the mass of the weight and the 'tensility' of the bar. I suppose I want to understand how a bending moment gives this kind of measurement of the torque.

My opinion is that Einstein himself admitted his equations described a spacetime which was fluid, frictionless but nonetheless a medium that could bend and stretch. He didn't realise at first that gravitational waves could propagate through it, that spacetime is the field. Which I think about as the surface of a lake being the field that waves propagate on, the propagation occurs below the surface though, it's a three dimensional wave. Currently research into superfluid dynamics is hoping to probe the early state of the universe; when did inertia first appear? That kind of thig.

The liquid was water and the surface waves appeared after I put some in a large brandy bowl. Using the usual technique, rubbing around the edge of the glass, a radial pattern of standing waves was made. I could see little or no turbulence even at the perimeter of the liquid. Everything looked nice and smooth, a really nice spatial derivative. A good way to prove water is an elastic fluid.

I heard a prof say in a lecture on gravity, on youtube of course but it was a university in Germany, that a point is like dust. The Euclidean plane is dust, the only thing keeping all the points together is a relation. There isn't any "glue" between two points no matter how close they are.

HI there. I've been doing some repairs on my car recently and I found myself wondering about my torque wrench. It isn't a precision tool, but good enough for bolts in the chassis, or the wheel nuts. Anyway, I was thinking about what happens to a steel bar if you fix it horizontally at one end and hang a weight at the other. It bends down at the weighted end and this end is now at an angle to the horizontal. So what does this angle represent? I know a torque is perpendicular to the applied force, but where do I go from there?