I just did some very simple physics calculations (at the end of this message) and it appears that the simple movement of the bodies clearly yields let's water absorption with increased horizontal velocity. I believe that your results and "busting" of this myth are explained by 1) puddle splashing, 2) large lateral motions of arms, legs and head, and 3) the curving of the body w.r.t. the vertical.
1) Splashing water brings fallen water up onto the bottoms of the clothing,
2) Large lateral motions introduces a big surface area for catching more water.
3) A bent head and curved/slanted body greatly increases the area for the rain to fall on without substantial decreasing the forward surface area of the body.
My equations show that for speeds slower than the terminal velocity of water, the area on top should be minimized with the smallest vertical profile, while speeds in excess of this yield less water absorption as the body is tilted to increase the top surface area and thus minimize the frontal surface area.
This myth is not busted, and should be repeated with these three points addressed. I suggest that you conduct the run portion by:
1) Minimizing/eliminating the splashing, 2) Minimizing the movement of arms, head, and legs (range walk as they say in the Army, or in other words a very fast walk lacking the wild characteristics of running), and 3) Keeping the body straight vertically. I personally run through the rain with a mind to minimize splashes, minimize exposing extra surface area, and keeping my body fairly vertical.
The equations are as follows:
Q = rho * v, rho is the water density in air (constant), Q is the rate of absorption per unit of surface area, v is velocity
t = D / vx, t is the time for the trip, D is the fixed distance of the route, vx is the velocity of the subject in the direction of travel
m = Qy*Ay*t + Qx*Ax*t, m is the total mass absorbed, x and y subscripts refer to the directions of horizontal and vertical, respectively. The first term is the mass of water absorbed from the falling rain, while the second term reveals the mass absorbed from running into it.
m = (rho*vy) * Ay * (D/vx) + (rho*vx) * Ax * (D/vx) with substitutions from above equations
m = rho*D * (vy*Ay/vx + vx*Ax/vx) = rho*D * (vy*Ay/vx + Ax), thus small vx (walking slow increases the left term and gets you wet, while walking fast minimizes it and leaves you drier).
Subscribe to:
Post Comments (Atom)
No comments:
Post a Comment