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The attachement from the international libraries association is self explanatory. Although not specifically for scientific matters I thought it was particularly well presented and a good candidate as a sticky on this site.

You could try hot filtration. You might need a fairly high temperature to bring down the viscosity of the molten wax sufficiently. There are industrial filtration systems that could do this sort of thing, in principle at least. For example, earth treatment of certain grades of lubricating oil is a well-established procedure.

Probably just a rhetorical question, but interesting nonetheless. The answer, very much having to do with the excellent points made, is all about symmetry groups --from a mathematical physics perspective. In economics, eg., you have graphs representing marginal utility --dimensionless, if I remember correctly-- plotted against number of units of goods --again, dimensionless. In electrical engineering tho, you have graphs plotting intensity against voltage --both dimensionful. But the subtle mathematical point is that in neither of those cases is there a group of symmetry relating different, but equaly valid, observational stances --classes of valid observers. In the physics of space-time, there is such class of valid observations, and the measurements of time and space of one observer are mixed up with the measurements of time and space of another, so it is natural to define the parameters of the transformation as dimensionless numbers. You could insist that (I,V) (intensity and voltage) be a 'vector', but it doesn't make much sense unless you can define transformations that take one stance to another and relate them in a linear way: I'=aI+bV V'=cI+dV with a,b,c,d being the dimensionless parameters that mix them up. That's the reason why in mathematical physics you tend to be more careful and say: Such and such quantities are a vector under SO(3) (rotations); or a vector under O(3) (rotations and inversions-reflections), etc. In the case of Minkowski vectors, it's all about inertial observers. It's what we call the 'Lorentz group'.

Do you have any data to support that claim? I ask because when I was a kid through young adulthood I remember cars breaking down regularly, not starting, and being ready for the junk pile by the time they hit 100,000 miles. The biggest issue I can think of with my past several vehicles is a light that went out on display, and all those I got rid of still ran fine when sold with over 150K miles on the odometer.

They are now. Before they were invented, nobody complained. Once a new thing - gizmo, convenience, extra little perk - becomes available, the people willing and able to do so pay extra for them. Then the manufacturers, hoping to charge more for all their products, spend a fortune of advertising that links these perks to the perception of success, and the people (usually staring with youngish middle-management) who want to be successful and try very hard to appear successful, buy whatever pricey product a celebrity is endorsing. When enough people buy it, the manufacturers can lower the price (still above the previous price, but not beyond to average buyer's credit limit) and in a few more years, make some of the desirable features standard - so the buyer no longer gets the option of not having it. For the next model, then, they have to come up with a new 'extra' for the elite wannabes, until that becomes standard.... The consumer is so used to having his gimme buttons pushed, he doesn't even notice.

Basically, the concept is meaningful only if it is independent of the specific path taken between the two events. This requires the presence of certain symmetries - which not all spacetimes have. For example, consider what happens if the spacetime is not stationary, such as in a binary star system. The work required to escape to infinity from any point within this system depends not only on where that point is, but also on when the escape happens, and what specific trajectory is taken. In other words, it depends on the path taken through spacetime, the metric of which now explicitly depends on both time and space coordinates. As such it isn’t possible to assign a single unique value that signifies gravitational potential to any point in that spacetime.

! Moderator Note We don't delete anything, but we also won't direct traffic to obviously incorrect science. I will ban you though. Sorry, but I hope you have horrible luck with that website of yours, and I hope you don't mess up too many of your fellow humans with your ignorant misinformation. Please study some science.

Yes, is is the famous square root of minus 1 [math]i = \sqrt { - 1} [/math] The purpose of i is twofold. To rotate the axis in an imaginary direction. To turn a + into a minus, so not i does not appear on both sides of the equation since [math]{(ict)^2} = {i^2}{c^2}{t^2} = - 1{c^2}{t^2} = - {c^2}{t^2}[/math] Yes I am going to take time out of explaining graphs and frameworks and also because sometimes a peek ahead is motivational and I propose to use the just the x and t axes for this peek. I was going to say that If you are an electrical engineer, that I hope you know enough mechanics to work from Newton's laws to the Principle of Relativity. However you have answered that so I will introduce the diagrams. Nowhere is this more true than in Relativity. It is worth knowing that there are lots of different ways to arrive at SR and GR, but they all start with two basic Principles for SR and a third is added for GR. Different authors express these Principles in different ways, most suitable to their route. The strategy I am following is to look for relationships where one measurement is identical to another. Such situations lead to invariants. One such is called the form invariant, which is employed in the Principle of Relativity The idea is that a physical law must not depend upon the coordinate system. That is it should have the same form in all relevant coordinate systems. As an example take two particles A and B, interacting though some force F(xA, xB) and consider their equations of motion in one dimension (the x axis) Newtons tells us that if mA and mB are their respective masses and xA, xB their x coordinates then [math]{m_A}\frac{{{d^2}x}}{{d{t^2}}} = F\left( {{x_A},{x_B}} \right)[/math] and [math]{m_B}\frac{{{d^2}x}}{{d{t^2}}} = - F\left( {{x_A},{x_B}} \right)[/math] Now suppose we describe these same two particles in acoordinate system whose origin is at x0 in the original system and call this new system the x' system. Then xA = x'A + x0 and xB = xB + x0 Substitute these two equations into the first two we get [math]{m_A}\frac{{{d^2}x'}}{{d{t^2}}} = F\left( {x{'_A} + {x_0},x{'_B} + {x_0}} \right)[/math] and [math]{m_B}\frac{{{d^2}x'}}{{d{t^2}}} = - F\left( {x{'_A} + {x_0},x{'_B} + {x_0}} \right)[/math] since x0 is a constant [math]\frac{{d{x_0}}}{{dt}} = 0[/math] So the forces of interaction do not have the same form (are not form invariant) as in the original coordiante system. If they did they would be [math]{m_A}\frac{{{d^2}x'}}{{d{t^2}}} = F\left( {x{'_A},x{'_B}} \right)[/math] and [math]{m_B}\frac{{{d^2}x'}}{{d{t^2}}} = - F\left( {x{'_A},x{'_B}} \right)[/math] And the new equations depend upon the origin x0 of the new system. So Newton's equatiosn, as they stand do not conform to the Principle of Relativity. However all is not lost. the remedy is to work with coordinate differences, not directly with the coordinates so we write F(xA,xB) = f(xA - xB) yielding equations of motion in the new system in the required form [math]{m_A}\frac{{{d^2}x'}}{{d{t^2}}} = f\left( {x{'_A},x{'_B}} \right)[/math] [math]{m_B}\frac{{{d^2}x'}}{{d{t^2}}} = - f\left( {x{'_A},x{'_B}} \right)[/math] This is the motivation for using the pythagorian square root of the sum of the squares of the coordinate distances I mentioned in an earlier post.

The term (ic) has to be appended to the t term for calculating the interval length, which has to be a 'distance' in space-time. It does not need to be appended to a space-time diagram, as it will not change the shape of any 'curves' plotted in your space-time diagram. Try it with X and Y on graph paper, then substitute 2X for every X value. The only thing affcted is the spread along the X axis. The difference on a space-time diagram would be that the diagonal ( representing the boundry between spacelike and timelike motion ) has a slope of 1 instead of c .

Please do, mr big stuff. And delete my two posts as well.

The urban driving speed in my country is currently 50 km/h, which is only +5 km/h more than 30 miles/hour. Who uses an electric car for longer trips when when you can't easily find plugs/unsure they are in place where you want to go.. ? ps. Many such speed regulations make no sense and have no real impact on road safety.. They are pushed by politicians who have no idea what they are doing, to pretend that they are doing something.. Electric cars, thanks to the energy stored in their batteries (which is good, if everything is OK), burn like they are "made of paper" after even a basic accident..