p.
  When building a simulation, you frequently want to refer to
  a group of Particles, Forces, and Constraints as a single entity.
  Newton uses the concept of Bodies for grouping elements.
p.
  Instead of adding Particles and Constraints directly to the Simulator,
  we can instead add them as a group in a Body:

pre.CodeBlock.
  var rope = Newton.Body();

  rope.add(Newton.Particle(500 + i * 20, 180));
  rope.add(Newton.RopeConstraint(prev, current));

  sim.add(rope);

p.
  Keep in mind, Bodies are just for bookkeeping - logical groupings so your code can be readable.
  They have no impact on the simulation.