The wetness and efficiency of walking
Stories from Physics for 11-14 14-16
A long-standing debate has focused on whether you will get wetter if you run or walk in the rain. Proponents of the ‘running will keep you drier’ hypothesis argue that it minimises your exposure to the rain, but those who favour walking as the drier option counter that runners will incur extra wetness on their front surface. Two published analyses suggest that running is the better option. It is reported that people who run will remain 30-50% drier than those who walk, especially in heavy or windy rain conditions. Another analysis suggested that the most effective solution was for the pedestrian to run at their maximum velocity, regardless of the speed of the rain or their dimensions. However, a paper in the European Journal of Physics argued that the effect was dependent on the shape of the walker.
In terms of energy expenditure, a study concluded that the peak efficiency of walking (between 35-40%) occurred at intermediate speeds, whereas the efficiency of running increases with speed (from 45% to 80%). Humans will typically switch their gait from walking to running at speeds somewhere in the range of 6.8 - 7.9 km/hr. Walking and running are both much less efficient approaches to locomotion than the motion of birds and fish.