dWorldID world = dWorldCreate();

  // Create a body
	dBodyID body = dBodyCreate(_world);

	dMass mass;
	dMassSetBox(&mass,1,1,1,1);
  dMassAdjust(&mass,0.2f);

	dBodySetMass(body,&mass); 
	dBodySetPosition(body,0,6,0);

  // Create another body
  // ...