How does the weight of a train influence its traction capability?

The weight of a train plays a significant role in its traction capability, particularly regarding the forces required to start moving and to maintain speed. Heavier trains necessitate more tractive effort due to their greater mass, which results in higher inertia. This means that additional force is needed to overcome the static friction when initiating movement and to counteract the increased resistance created by the train's weight when moving along the tracks.

Moreover, as weight increases, the adhesion between the train wheels and the track surface can be affected. A greater weight can indeed enhance the grip, but this is contingent upon the locomotive’s ability to effectively utilize that weight without sliding. Therefore, more tractive effort is required not only to initiate motion but also to sustain acceleration and maintain desired speeds, particularly when encountering inclines or curves.

In summary, the correct option emphasizes the direct relationship between a train's weight and the amount of tractive effort needed, illustrating the fundamental principles of physics that govern train operations.