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JavaScript

/*
(Book REF) HTML5 Canvas Ch. 5:  Math, Physics, and Animation ::: Uniform Circular Motion
By Steve Fulton and Jeff Fulton
*/
window.requestAnimFrame = (function() {
  return window.requestAnimationFrame ||
    window.webkitRequestAnimationFrame ||
    window.mozRequestAnimationFrame ||
    window.oRequestAnimationFrame ||
    window.msRequestAnimationFrame ||
    function(callback) {
      window.setTimeout(callback, 1000 / 60);
    };
})();
window.addEventListener('load', start, false);

var c,
  $,
  w,
  h,
  msX,
  msY,
  midX,
  midY,
  num = 650,
  parts = [],
  begin = 50,
  repeat = 20,
  end = Math.PI * 2,
  force = null,
  msdn = false;

function start() {
  c = document.getElementById('canv');
  $ = c.getContext('2d');
  w = c.width = window.innerWidth;
  h = c.height = window.innerHeight;
  midX = w / 2;
  midY = h / 2;
  force = Math.max(w, h) * 0.09;
  flow = begin;

window.requestAnimFrame(create);
  run();
}

function run() {
  window.requestAnimFrame(run);
  go();
}

function Part() {
  this.deg = 0;
  this.rad = 0;
  this.x = 0;
  this.y = 0;
  this.distX = 0;
  this.distY = 0;
  this.color = 'rgb(' + Math.floor(Math.random() * 130) + ',' + Math.floor(Math.random() * 50) + ',' + Math.floor(Math.random() * 100) + ')';
  this.size;
}

function create() {
  var n = num;
  while (n--) {
    var p = new Part();
    p.deg = Math.floor(Math.random() * 360);
    p.rad = Math.floor(Math.random() * w * 0.5);
    p.x = p.distX = Math.floor(Math.random() * w);
    p.y = p.distY = Math.floor(Math.random() * h);
    p.size = 1 + Math.floor(Math.random() * (p.rad * 0.055));
    parts[n] = p;
  }
  c.onmousemove = msmv;
  c.onmousedown = msdn;
  c.onmouseup = msup;

var int = setInterval(function() {
    flow--;
    if (flow === repeat) clearInterval(int);
  }, 20);
}

function msmv(e) {
  var p = getPos(e.target);
  var sX = window.pageXOffset;
  var sY = window.pageYOffset;
  msX = e.clientX - p.x + sX;
  msY = e.clientY - p.y + sY;
}

function msdn(e) {
  msdn = true;
}

function msup(e) {
  msdn = false;
}

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