Rolling a Drum vs Carrying Water: Pull Force, Gradient, Step, and Time Bounds for a 90 Litre Drum on Dirt Paths

Rolling a water drum instead of carrying containers is widely promoted for households that fetch water on foot, but the advantage has limits that are rarely stated in numbers. This paper computes them for a 90 L drum (98 kg gross, 0.50 m diameter) on dirt paths. The level pull is 48.1 N on firm packed dirt (rolling coefficient 0.05), 96.1 N on ordinary soft dirt (0.10), and 173.0 N on very soft dirt (0.18), against a stated sustained one-person pull limit of 100 N. The gradient at which the required pull reaches that limit is 5.42% on firm dirt and only 0.40% on ordinary soft dirt; on very soft dirt the drum is already over the limit on the level. A step is a harder barrier than a slope: a horizontal pull at the axle needs 721.0 N to lift the drum over a 50 mm step, 465.6 N over 25 mm, and even a 10 mm lip needs 280.4 N; the step that a sustained 100 N pull can climb is 1.3 mm. Where the path suits it, rolling is far faster: fetching 90 L over a 500 m path takes 16.2 minutes by drum against 73.7 minutes in five 20 L carrying trips, walking 1.0 km against 5.0 km. Rolling therefore wins decisively on gentle, firm, step-free paths, and loses — stated plainly — on steep paths, on any path with steps or kerbs, and on very soft ground.