Final answer:
The perpendicular force in a free-body diagram has a relationship with the other forces involved. The hypotenuse of the triangle formed by the perpendicular forces is the resultant force, and the opposite and adjacent sides are relevant as they represent the components of this resultant force. The adjacent side is never irrelevant as long as it is contributing to the overall force.
Step-by-step explanation:
The question relates to Physics, specifically understanding forces and vectors. In the context of the question, when you are drawing the perpendicular force, it's important to recognize certain characteristics of the forces in a free-body diagram. When two force arrows are drawn at a right angle to one another, they act perpendicularly. In this case, if we apply the Pythagorean theorem, the hypotenuse represents the resultant force of the two legs of the triangle, which are the two perpendicular force vectors. The opposite and adjacent sides to the angle represent the components of the resultant force. The adjacent side is not irrelevant; it is one of the components contributing to the overall force.
In a scenario where forces are at equilibrium, such as in a situation with a block on a spring on a frictionless surface, the weight and the normal force are equal in magnitude and opposite in directions, canceling each other out. The force due to the spring, however, acts parallel to the surface and is the net force acting on the object. If the directions of the forces are at a 90° angle to each other, this situation will satisfy conditions for equilibrium.