   XNA Platformer - first time using Physics
  Hey, I've been doing XNA for a while now, I've done about 4 full(albeit very simple) games. Pong, Breakout, Pickin' Sticks, and Tetris.Now I'm trying to make a platformer, and I simply cannot figure out the physics of jumping. So far I have a little Mario sprite that I can walk back and forth fully animated and all that good stuff, but the best I can do as far as jumping goes is make him go up a certain number of pixels, then come back down. That sounds good, but it looks really jerky and totally freaks out when I try to move while doing that at the same time. And then I accidentally deleted that and forgot how I did it, so I'm at square one.Could someone just point me in the right direction as far as getting my feet wet in gaming physics with XNA? I have a rudimentry knowledge of real-world physics, so I know what's actually going on in a jump, I just have no idea how to implement that.   
  I take it you already know about your equations of motion:v = v0 + at(Velocity equals: initial velocity, plus acceleration (usually gravity) multiplied by time.)s = s0 + v0t + ½at²(Displacement equals: initial displacement, plus initial velocity multiplied by time, plus half acceleration multiplied by time squared.)In any case, this article of mine may help. (I recommend you save a copy, because I'm moving my website shortly.)You haven't really asked a good question (perhaps next time post some code) - so I'll just give you some quick pointers:Use a fixed time-step (XNA should do this by default anyway).You should be treating X and Y independently (for your first platformer, simply allow air movement at the same speed as ground movement) - so jumping shouldn't cause any problem with horizontal movement.If collision detection is a problem - it's probably best to start with no "world" as such and just treat Y=0 as the "ground". Also: avoid slopes in your first platformer - just make one with a blocky world (it worked for Knytt). And don't even think about using an actual physics engine - it's stupidly difficult (been there, done that).As far as accidentally deleting stuff goes: please download, install and learn to use Subversion and TortoiseSVN. This is possibly the best thing you can do as a developer.   