Climbing Completely Verticle Surfaces: The Physics of Crag Climbing

     I have done rock climbing since the beginning of high school and really love it. As it is finally becoming a part of the Summer Olympics, I thought I would share one of my favorite niche aspects of the sport. Crag climbing is the act of using a vertical crack in a wall in order to climb up. This requires putting your hands and feet into the crack in order to not only support your weight, but provide enough force to climb as well.

     In doing this, there is practically nothing directly beneath you to hold your weight up. Rather, your weight must be held up by friction from the sides of the wall alone. Rock climbers have figured out a pretty effective way of dealing with this problem by maximizing the amount of frictional force that they can get from the wall. I admit it is not easy to find a picture of this, but you can see it a little in the provided pictures.

     Crag climbers will not only stick their hands and feet into the wall, but maneuver them in a very specific way. For their hands, they will place them in sideways and press out with their fingers. This ultimately allows the climber to force the back of their hand against one side of the crack while keeping their fingers on the other. As for their feet, they will be placed in sideways at first. They will then rotate their foot until it is once again parallel with the ground, effectively forcing the sides of their feet to squish against either side of the crack. These two tactics work perfectly together to increase the total frictional force by increasing the force applied to the wall.

Fapplied = Fnormal

Ffriction = μFnormal

     Following the laws of physics regarding friction, it is clear that the increase in applied force in the x direction increases the corresponding normal force, and hence the force of friction acting in the y direction. Therefore, if the climber is strong enough (keep in mind this is very difficult and really hurts your hands), they can apply enough force outwards that they are able to climb a completely vertical wall.