Final answer:
The direction and magnitude of the effort force in a first-class lever depend on the distances from the fulcrum to the points of force application, and it's related to the mechanical advantage offered by the lever in accordance with Newton's second law.
Step-by-step explanation:
If the resistance force of a first-class lever moves in a specific direction (up or down), we can deduce certain properties about the effort force. A first-class lever is structured such that the fulcrum is located between the effort and resistance forces. When we apply the effort force on one end, there is an equal and opposite reaction force which, in a static scenario, balances out the effort force. The mechanical advantage of the lever indicates how much the lever amplifies the effort force to move the resistance force. The greater the distance from the fulcrum to where the effort force is applied (effort arm) compared to the distance from the fulcrum to the resistance (resistance arm), the larger the mechanical advantage. Using the concept of Newton's second law, we understand that the direction of the acceleration is determined by the net external forces acting on an object.