p.
  Just like add() adds Particles, Forces, and Constraints to a simulation,
  remove() removes them.

p.
  In this case, we want to remove the PinConstraint whenever the user releases her mouse,
  so she can "let go" of the dragged Particle:

pre.CodeBlock.
  renderer.on('pointerup', function(point) {
     if (!mousePin) return;
     sim.remove(mousePin);
     mousePin = null;
  });