1. The problem statement, all variables and given/known data The physics of circular motion sets an upper limit to the speed of human walking. (If you need to go faster, your gait changes from a walk to a run.) If you take a few steps and watch what's happening, you'll see that your body pivots in circular motion over your forward foot as you bring your rear foot forward for the next step. As you do so, the normal force of the ground on your foot decreases and your body tries to "lift off" from the ground. (a) . A person's center of mass is very near the hips, at the top of the legs. Model a person as a particle of mass m at the top of a leg of length L.Find an expression for the person's maximum walking speed vmax. Express your answer in terms of the variables L and appropriate constants. 2. Relevant equations 3. The attempt at a solution Now I have the solution, which is reached in the following way: mg - N = (mV^2)/r N = 0 at Vmax. Also, let r = L. mg = (mV^2)/L Vmax = sqrt(Lg) = Answer. Now what I don't understand is why is it mg - N, rather than N - mg, seeing as how mg is pointing down and N is pointing up? Thanks.