Question

What is the difference between a stabilizing force and dislocating force? At what angle of pull does the stabilizing force become a dislocating force? Why? For full credit, draw the free body diagrams and equations of force or moment to support your answer.

Answer 1

STABILIZING FORCE	DISLOCATING FORCE
The component of muscle force that acts parallel to the attached bone	The force acting on a dislocation is not a physical force like mechanical force but a way to descrie the tendency of dislocation when external and internal stresses present.
The angle of pull is 900	The angle of pull is above 900
Stabilizing force towards fulcrum	Dislocating force is away from the fulcrum
In this all the force produced by the muscle directed back into the joint, pulling the two bones together	The force produced by the muscle directed away from the joint, making them them to move away from each other

ANGLE OF PULL: It is the defined as the angle between the line of pull of the muscle and the bone on which it inserts.

• Most of the resting muscles have angle of pull less than 90⁰ and it is indicated by joint angle .
• Above 90⁰ the stabilizing force become a dislocating force because as the joint angle decreases between the bones when the muscle force increases . After 90⁰ the muscle force  increases because it works against gravity so joint angle decreases leading to dislocation.

Here,F_m  represents moment of force which is defined as the product of force and perpendicular distance from the line of action and point where theobject turn.

The Magnitude of moment of force is directly proportional to magnitude of acting force and distance of point from line of action.So when the magnitude of force increases, the muscle angle with the joint increase as above said the, angle of pull >90 leads to dislocation.