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 Mar 14 comment Does Angular Momentum change what I change Center Of Mass? That's not really the problem. We don't know how your physics engine works, if it's force based, impulse based, etc. We don't know why you even need to know the center of mass of an object, or its angular momentum, or what you could be doing with those quantities. Besides, most physicists aren't the best people to ask if you're trying to write a real-time physics engine (if you have 100 bodies interacting, a physicist might tell you to solve a $100^2$ size matrix equation each frame, whereas a game developer would tell you to use a lightning fast "good enough" approach). Mar 14 comment Does Angular Momentum change what I change Center Of Mass? This is completely impossible to answer without knowing the numerical details of your simulation/what you mean. The center of mass is $\frac{1}{M}\sum_i m_i \vec{r}_i$, and this changes if you add another $m_i$ and another $\vec{r}_i$. The angular momentum is $\sum m_i \vec{r}_i\times\vec{v}_i$, and this will change if the particle you add has nonzero velocity. But "you have to offset the x,y,z of an object when you change center of mass" is a totally nonsensical statement. It may make perfect sense in the context of your physics simulation, but it's completely meaningless to the rest of us! Mar 13 answered Perspective Redux (why objects seem smaller as the distance increases) Mar 11 comment Rational for the Principle of Relativity @afuna Maxwell's equations are invariant under a Lorentz transformation, but they aren't invariant under a Galilean transformation. So they don't mathematically prove anything about physical transformation laws. As a simpler example, consider $\phi_{tt}(x,t)-\phi_{xx}(x,t)=0$ where $\phi$ is a function and subscripts denote partial derivatives. This is a wave equation. It can represent ripples on a pond (a situation where Galilean transformations are appropriate) or electromagnetic waves (a situation where Lorentz transformations are appropriate). Mar 11 comment Rational for the Principle of Relativity You say it seems anthropocentric... but general and special relativity are anything but! To phrase it dramatically: the hubris of Newton was to lay a coordinate system out over time and space of the whole universe and assume how it works! As you study special relativity more, and notice the similarities between Euclidean geometry ($x^2+y^2$ versus $x^2-(ct)^2$), you'll start to appreciate it more. Galilean and Lorentzian geometry are incredibly similar, and it's not up to us to decide which one the universe uses. Mar 10 comment Entropy change in a boiling egg After the egg has cooled down and is in equilibrium with its environment? Mar 9 comment Boiling as apparent violation of the second law of thermodynamics @AyanBiswas Of course energy is still conserved. Mar 7 awarded Enlightened Mar 4 comment Is time a vector in Minkowski space? Like many arguments with teachers, it depends on your definitions. The timelike coordinate is a component of a vector, so it's a vector. But vectors are objects over scalar fields, so it's a scalar. But you could also define the object "$t$" as a timelike unit vector $t$ (For which $t^{\mu}t_{\mu}=-1$), so it's a vector. But in general relativity you can regard coordinates as scalar functions over a patch on your manifold, so it's a scalar. :P It's basically just arguing over a definition. Mar 3 awarded Revival Mar 2 comment Question about 3d collision of 2 particles Possible duplicate of Determine resultant velocity of an elastic particle-particle collision in 3d space. Please see my answer on that page Mar 2 comment What would happen if another big bang occurred at the centre of the current universe? The big bang happened everywhere at once ( youtube.com/watch?v=W4c-gX9MT1Q ) so this question isn't well-defined. Mar 2 comment Planets potential closer! But the centrifugal force is an imagined one whose only purpose is to make the same formulas work in a rotating frame of reference. You can't really understand it without really going through Newtonian mechanics. Mar 2 comment Planets potential Well, basically Lennard Jones and general relativity have nothing to do with it! Think of swinging a string with a ball on the end of it around over your head. the only force on the ball is inwards, towards your hand, and yet it's stable! You don't need an outwards force. The same is true for the moon/earth or earth/sun, but the force isn't from string, it's from Newtonian gravity. khanacademy.org/computer-programming/… Mar 2 comment Planets potential Hi! I think you should worry about studying Newtonian Mechanics, which requires calculus to learn. Right now you're thinking a lot of things that just aren't physics, and are misunderstanding a lot of concepts. Maybe study a bit of calculus (to where you can differentiate/integrate simple functions), and then get the book Newtonian Mechanics by A P French. Mar 1 comment Does light in vacuum actually travel at the speed of light? @GeniaS. I'm certain that, if pressed, Michael Enciso would tell you that he reached that conclusion through the limiting procedure I went through in my post. I covered all my bases! :) Mar 1 comment Does light in vacuum actually travel at the speed of light? @GeniaS. The way I see it my answer still stands. You want to know what a photon sees in its own frame of reference. Special relativity says that's an ill-defined question because there is no such frame of reference. You go wrong as soon as you say, "if I were a photon", because right then you presume a frame of reference exists. (And the big bold point of this post is that that frame doesn't exist!) Feb 29 reviewed Approve Biot-savart's Law and mass of an electon Feb 29 reviewed Approve Liquid conductors and conservation Feb 29 revised Does light in vacuum actually travel at the speed of light? added 202 characters in body