Final answer:
A single force with the same effect in magnitude and direction as multiple forces is known as a resultant force. Forces in equilibrium have equal magnitudes but opposite directions and act on different systems in accordance with Newton's third law.
Step-by-step explanation:
A single force which acting alone will have the same effect in magnitude and direction as two or more forces acting together is called a resultant force. When considering two forces that act on a point in equilibrium, these forces have equal magnitudes but act in opposite directions. According to Newton's third law, every action force is met with an equal and opposite reaction force, but these forces act on different systems and do not cancel each other out because they are not acting on the same body. In the context of most situations involving forces, we also differentiate between contact forces (direct physical interactions) and field forces (forces acting over a distance due to a field, such as gravity). A resultant force is a single force that has the same effect as two or more forces acting together. It combines the magnitudes and directions of individual forces to represent their overall effect on an object. If the forces are balanced, the resultant force is zero, and if the forces are unbalanced, there is a nonzero resultant force that causes acceleration or changes in motion.