So when the train moves clockwise, the wheel moves counterclockwise with an equal and opposite angular momentum. When the train stops, the wheel stops. When the train backs up, the wheel moves forward. Without the small rotor on its tail, the helicopter and the main rotor would rotate in opposite directions. The small rotor offsets the rotational motion that the helicopter would otherwise have.
Gravitational force acting on every particle by every other particle causes the cloud to condense.
The decreased radius of the cloud is then accompanied by an increased angular speed because of angular momentum conservation. The increased speed results in many stars being thrown out into a dish-like shape.