I’ve been competitively running for almost 10 years now and have really never thought about the physics behind running. I just lace up my shoes and run what my coach tells me to. This is why I decided to look into the physics of running, since I do it daily. For starters, there is the force of gravity that is pulling the runner down from their center of mass and then there is the force in the x direction which is what causes the runner to move forward. There is also the force in the y direction which happens because of the contact that occurs between the foot of a runner and the ground. In order to run, the force in the y direction must be greater than the force felt by gravity. The speed at which a runner moves at is determined by the magnitude in the x direction. Thus the greater the force in the x-direction, the greater the speed of the runner.
It is also important to take into account that arms play an important role when running. When a runner’s foot makes contact with the ground, the force in the x direction causes torque 1 to move the torso of the runner inward. To counteract this torque, a runner swings their arm simultaneously in the direction opposite to that of torque 1. Thus, causing stability and forward motion of the runner. Furthermore, bent arms are the most efficient way to swing them. When thinking about pendulums, the smaller a pendulum, the easier it is to move therefore, it’s more efficient to run with bent arms. This is the physics behind the activity that I love to do.