An automated overhead gantry crane raises a heavy cylindrical containment capsule vertically out of an industrial salt brine storage pool during a decommissioning process.
The capsule is raised at a constant speed, even though the tension (lifting force) in the hoist cable changes over time.
Figure 1 shows how the lifting tension varies during this recovery process.
Explain why the lifting force changes as shown on the graph in Figure 1. Include calculation(s) in your answer.