text: Steam locomotives were huge railroad engines that drew long "trains" of railroad cars.  The word locomotive stems from Latin locus (place) + motio (motion).  Dimensional analysis is used to test scale models of steamships (etc.) that can be towed in model tanks to discover how the full-sized ship will perform (before it is built!).  For example, water exhibits a surface tension that may have nil effect on a large ship but must be accounted for on the model to correctly interpret test results.