The discussion focuses on determining when to add or subtract forces such as normal, kinetic friction, and tension when calculating the net force (\Sigma F) in both horizontal and vertical directions. Key principles include recognizing that gravity always points downward, friction opposes motion, and normal force acts perpendicular to surfaces. The use of standard angle notation is emphasized, where all forces are added, and a negative magnitude indicates a need to adjust the angle by adding 180 degrees. Understanding the sign convention is crucial, with upward forces considered positive and downward forces negative in vertical calculations.
PREREQUISITESThis discussion is beneficial for physics students, educators, and anyone involved in mechanics or engineering who seeks to understand the application of forces in various contexts.
I will assume that you know how to determine (by inspection) the actual direction of a force and how to find its components. (TVP45 gave some advice in that regard.) As far as whether you add or subtract a given force when finding the net force, that depends on your sign convention. For example, consider vertical forces. If you take the usual convention where up is positive and down is negative, then any downward force will be negative when adding vertical forces. For horizontal forces, to the right is often positive and to the left is negative.p4cifico said:...how do I know when to subtract or add these forces from [tex]\Sigma[/tex] F (x or y) ?