You'll have to excuse me if this issue has been discussed here before. I did about 30 minutes worth of searching and didn't come upon it, so I decided to post. A colleague and I had a lengthy discussion today on whether running a set distance spends more calories (energy) than walking that same distance. My main argument centered around moving a mass over a distance. My contention is that work is the product of force and distance: W = F * d If the same mass, m, is moved across the same distance, d, then the same force, F, is exerted. The hinge point of my argument is the assumption that your acceleration/deceleration is instantaneous. If you look at the free body diagram, you'll note that you have force acting in two axis on the mass. In the x-axis, you have the applied force, F, and the friction force, F_f. According to Newton's Second Law, a body in motion will stay in motion unless acted upon. Hence, in order to keep a constant velocity, F = F_f hence [tex]\Sigma[/tex] F_x=0 In the y-axis, there's a gravitational force, F_g = m * g and the equal and opposite normal force, F_N F_g = F_N hence [tex]\Sigma[/tex] F_y=0 The kinematic coefficient of fricition, u, is the same, regardless of velocity. The equation for friction force is: F_f = F_N * u * cos(theta) <-- Theta being the angle at which the plane the mass is on is at. Assume a flat plain (cos0 = 1) for simplicity here. Regardless of velocity, u and F_N are the same, hence F_f is the same. So, if F_f is the same, F is the same. And, in the end, W = F * d produces the same product regardless of velocity. In the end, I convinced my coworker that my approach was correct. Although, he didn't buy the end result. I'd love to hear some of your thoughts on this subject.