Re: [Phys-L] raining
at 2:43 a.m. this morning, a note from David said in part:
"Assuming a temporally and spatially constant/uniform density of rain water in
the air (and an upright posture) then the amount of rain striking your head and
shoulders (and any surface with a horizontal projection) from above will be
proportional to the time you spend out in the rain. "
This speaks for the virtue of running fast over a fixed distance in order to
minimize wetting.
If the upright posture requirement is waived, we can suppose that walking or
running is a dynamic state of toppling interrupted by upthrust from the forward
foot.
In this case, the attractive concept of sweeping constant frontal area X
distance can be modified by the slight frontal area reduction provided by
toppling forward at a constant angle alpha, so that the reduction in swept
volume is 1 - cos alpha - a rather modest reduction..
Consider a second factor: that running describes a saltating waveform. David's
concept of constant spatial rain mass density clarifies that this does not
affect the forward rain volume intercepted.
Hence body tilt further favors faster movement in rain.