A VectorForce is used to apply a force to a part or assembly of parts. The direction and strength of the force is determined by a Vector3 and can be relative to an attachment on the part, another attachment, or the world coordinate system.
The following image demonstrates how VectorForce applies a force on a part relative to an Attachment.
The following image demonstrates how VectorForce applies a force on a part relative to the part's center of mass.
Location of force
When VectorForce.ApplyAtCenterOfMass is false, which it is by default, the force will be applied to the part at the Attachement0's location. This means that if the attachment is not at the center of the part, it can create a torque on the part.
When ApplyAtCenterOfMass is set to true, the force will check if any other parts are rigidly connected to the parent part of its Attachment0. If there are, then the force will apply at the center of mass of all of the connected parts. If there are no rigid connections to other parts, the force will simply be applied at the center of mass of the part.
Direction of force
The direction of the force is determined by the Vector3 defined by force, but it will also be affected by the VectorForce.RelativeTo property.
By default, VectorForce.RelativeTo is set to Enum.ActuatorRelativeTo.Attachment0, meaning the force will be applied in the space local to the attachment. Remember that when visualizing an attachment, the yellow arrow shows the direction of positive X, and the orange bar shows the direction of positive Y. If the part the attachment is connected to rotates, the force will change direction to make sure it is still in the context of the attachment.
RelativeTo can also be set to Enum.ActuatorRelativeTo.Attachment1. In this case, the force will be applied in the space local to Attachment1, regardless of the orientation of Attachment0 or its connected part. If Attachment1 rotates, then the force will change to stay oriented correctly.
Lastly, RelativeTo can also be set to Enum.ActuatorRelativeTo.World. In this mode, the force is applied in world coordinates, regardless of the orientation of Attachment0 or its part.