D3 Bubbles!

bubbles.js

w = 960,
h = 500;

var svg = d3.select("body").append("svg:svg")
    .attr("width", w)
    .attr("height", h);

var circle = svg.selectAll("circle")
    .data(d3.range(70).map(function(datum,interval) {
      return {
        x: interval*20,
        y: 0,
        dx: 5,
        dy: -3 * (Math.random()+1),
        mu: Math.random()*2
      };
    }))
  .enter().append("svg:circle")
    .attr("r", 2.5)
    .attr("fill","blue")
    .attr("opacity",".5");

var text = svg.append("svg:text")
    .attr("x", 20)
    .attr("y", 20);

var start = Date.now(),
    frames = 0;

d3.timer(function() 
{

  // Update the FPS meter.
  var now = Date.now(), duration = now - start;
  text.text(~~(++frames * 1000 / duration));
  if (duration >= 1000) frames = 0, start = now;

  // Update the circle positions.
  circle
      .attr("cx", function(d) { d.x += Math.random()*3*Math.sin(Math.random()*3*d.x + Math.random()*10); if (d.x > w) d.x -= w; else if (d.x < 0) d.x += w; return d.x; })
      .attr("cy", function(d) { d.y += d.dy ; if (d.y > h) d.y -= h; else if (d.y < 0) d.y += h; return d.y; })
      .attr("r",function(d)
      {
        return (d.y < 100) ? d3.select(this).attr("r") : d.mu*500/d.y;
      });
});