Newton's Third Law: Newton's Third Law states that for every action, there is an equal and opposite reaction. This means that when one object exerts a force on another object, the second object exerts an equal and opposite force on the first.
Free-Body Diagram: A free-body diagram is a visual representation of all the forces acting on an object, including external forces, which is used to analyze the object's motion and the net force acting upon it.
Net Force: The net force is the vector sum of all the forces acting on an object, including external forces. The net force determines the object's acceleration according to Newton's Second Law.