p.
  In most cases, you'll extend Newton's base Body to create reusable custom Body types.
  For example, let's create a Rope Body:

pre.CodeBlock.
  function Rope(x, y, length) {
    Newton.Body.call(this);   // call Body's constructor

    // implementation here
  }

  Rope.prototype = Object.create(Newton.Body.prototype);  // extend Body's prototype

  var rope = new Rope(225, 10, 300);