Which of the following is a necessary condition for applying the vibratory roller effectively?

Amplitude is a crucial factor in the effective application of a vibratory roller. The amplitude refers to the height of the vibrations generated by the roller as it operates. This parameter significantly influences the compaction process because it determines how deeply the vibrations can penetrate the surface being compacted. A higher amplitude can lead to better compaction outcomes by effectively breaking down the soil or material layers and packing them more tightly together.

When the amplitude is suitable for the specific material and thickness being compacted, it allows for efficient energy transfer and reduces the risk of leaving voids or weak spots in the compacted layer. Thus, using the correct amplitude ensures that the compaction is uniform across the surface, which is essential for achieving the desired density and strength in the roadway or base layer being prepared.

While other factors such as transverse movement, material thickness, and drum width may influence compaction, they do not have the same direct impact on the vibratory mechanism's efficiency and effectiveness as amplitude does.