Sometimes I have to ride standing up. Short travel from airport departure gate to airplane and in local bus and train journey necessitates me to ride on a moving platform standing up. Such rides are not always smooth, even after ignoring the bumps on the road, force of acceleration, deceleration and curvature throws off the person with weak support. Hence, to stabilize myself, I need to hold on to handrails or handlebars. One point support at top end of my body frame doesn’t provide me full steadiness and unless I have something to hold on to at my waist level by other hand, my posture is not firm. Such horizontal support is not easy to come by, particularly if there is paucity of handrails compared to people, if I am holding some piece of luggage with my other hand, or if I am lodged in the middle of crowded vehicle away from walled boundaries of said platform.
At such moments, which are far too common, I must brace myself using my feet. Knowing that bending moment of a cross section is function of cube of the height and of only width, I position my both feet in L shape so as to provide me maximum moment of inertia on two perpendicular direction. Any force of jolt from any direction can be adequately born by two mutually perpendicular frames of my leg by splitting the component of force along two axis defined by L shape. At least, this is hoped. On many such occasions, I observe position of feet of co-passengers and find no apparent logic or system to buttress against the swing of turning or stopping.
Irony of the matter is that despite my posture based on solid grounds of physics and dynamics, I’ve found myself more vulnerable to jerks compared to other people who exhibit no visible support better than me.