Which of the following contributes to a longer takeoff run?

A longer takeoff run is significantly influenced by the weight of the aircraft during the takeoff phase. When an aircraft carries excess weight, it requires a greater lift to become airborne. This increase in lift demand translates to needing a longer distance to reach the necessary speed for takeoff.

Excess weight affects not only the thrust-to-weight ratio but also the aircraft's ability to accelerate. Heavier aircraft will need higher speeds to achieve the same lift compared to their lighter counterparts. Consequently, the takeoff run is extended due to the delay in reaching these higher speeds.

In contrast, other factors like normal weight, lower air density, and a clean, dry runway can either maintain or improve takeoff performance, thereby not contributing to a longer takeoff run when compared to the impact of excess weight.