this.px = x;

  this.py = y;

  this.vx = 0;

  this.vy = 0;

  this.mass = mass;

}

Ball.prototype.collide = function(other) {

  this.vx = (this.mass - other.mass) / (this.mass + other.mass) * this.vx;

  this.vy = (this.mass - other.mass) / (this.mass + other.mass) * this.vy;

}

Ball.prototype.applyForce = function(x, y) {

  this.vx += x;

  this.vy += y;

}

Ball.prototype.update = function() {

  this.vx / this.mass;

  this.vy / this.mass;

  this.px += this.vx;

  this.py += this.vy;

}

Ball.prototype.draw = function() {

  circle(this.px, this.py, 32);

}

​

var balls;

​

function setup() {

  createCanvas(480, 320);

  balls = [];

  for(var i = 0; i < 1; i++) {

    balls.push(new Ball(random(0, width), random(0, height / 2), random(2)));

  }

}

​

function draw() {

  background(220);

  for(var i = 0; i < balls.length; i++) {

    var ball = balls[i];

    ball.applyForce(0, 2);

    ball.update();

    if(ball.px < 16 || ball.px > width - 16)

      ball.vx = -ball.vx;

    if(ball.py < 16 || ball.py > height - 16)

      ball.vy = -ball.vy;

    for(var j = 0; j < balls.length; j++) {

      if(j === i) continue;

      ball.collide(balls[j]);

    }

    ball.draw();

  }

}