Randall D. Knight — Dynamics II: Motion in a Plane: Problem 55

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 \(v_{max}\). b. Evaluate your expression for the maximum walking speed of an 85 kg person with a typical leg length of 80 cm. Give your answer in both m/s and km/h, then comment, based on your experience, as to whether this is a reasonable result. A “normal” walking speed is about 5 km/h.