Hi all, I am doing a project on the speed limit on human sprinting. I was doing a thought experiment and then got myself confused, so I hope you guys can help me out. I assumed that there is no air resistance, and that the coefficient of friction between the ground and the foot is sufficiently large such that no slipping will occur. Therefore, whenever the foot is on the ground, it will not move. When one runs, one swings the foot backwards against the floor, and it is the friction that moves the person forward. Since the foot is not moving when it is on the floor, if the person swings the foot backwards at speed v relative to itself, I believe it is reasonable to say that the person will move forward at speed v relative to the ground too. In that case, if we ignore air resistance, doesn't that mean we can keep on increasing the speed and reach extremely extremely high speeds? Also, I did a numerical simulation using excel, and found out that the drag force is actually not that big and rather insignificant because even Usain Bolt does not run fast enough for drag to become an important factor. Therefore, I would like to ask, why is it that humans run so slowly? Thanks in advance.