"contact" - mkraska/meclib GitHub Wiki

[ "contact", "name", [x, y], [dx, dy], targetRef, lineLength, visible ]

Point-type support representing a contact between the sketched body and an environment object that gets cut away. Whether the contact is smooth or rough (static or kinetic friction) is decided in the feedback, see Feedback for "contact". Appears as a gray cross (normal + tangent line) once the referenced object is deactivated.

• "name" label, typeset in MathJax math mode (may be empty)
• [x, y] contact point
• [dx, dy] normal direction vector (outward, need not be normalized); the tangent is perpendicular to it
• targetRef name (string) or 1-based index (integer) of the object that this contact replaces once cut away
• lineLength (optional, default 3) length of the gray cross indicating normal/tangent snap directions, in grid units (the default leaves 1.5 units on each side for a force arrow)
• visible (optional, default true) whether the gray cross is ever drawn; it is only shown while the referenced object is deactivated

Status (for names/free body diagram matching) is derived automatically from the referenced object: "hide" (eligible for a reaction) once that object is deactivated, "show" otherwise.

See Feedback for "contact" for feedback functions in free body diagrams.

Tip: a second contact at the same point with another direction (a dummy that no feedback checks) hides which of the gray crosses is the right one.