Friction = force generated in resistance to movement
There are two kinds of friction: static and kinetic.
- Static friction keeps objects from moving as long as the applied force is less than the static friction. Once the applied force exceeds the maximum static friction, an object begins to move.
- Friction remains in play here, but now it slows down a moving object, instead of keeping one in place. This kind of friction is called kinetic friction.
Friction in relation to rock climbing
In climbing, static friction is created against the rock (or plastic, wood, whatever you climb on) and our hands, feet, and body. If enough static friction exists, we can move against it and progress ourselves along a sequence; however, if we generate more force than the static friction, hands and feet slip, and we fall.
The amount of force friction generated and the type of force required to perform a move depend on the specifics of the rock type, shape, and texture, as well as your body’s orientation, environment, and a plethora of other factors.
Related: Don’t Take it for Granite: Understanding Different Rock Types
Some of these factors (often involving the rock), we cannot really control ( but how interesting it would be if we could just create a jug in the rock whenever we needed it!?). Other factors, however, we can control:
- Sweat reduces friction between our hands and rock, so we use chalk to help to dry out our hands.
- Hand position affects how we can apply a force, so we often test a hand hold different ways to see which way “feels” best and gives the most secure grip.
Related: 5 “Ninja Grabs” Every Climber Should Have
How and why your finger positioning affects frictional force
When applying a force with the fingers together, the forces generated from each finger are parallel with each other and perpendicular to the hand hold, which gives a maximum frictional force against which to pull.
With the fingers separated, the forces generated in each finger are not parallel; they are at slight angles. Because of these angles, some part of the applied force will try to move the fingers together.
When fingers remain separated, that means enough “sideways” friction was generated to keep them in place. This friction was not present before and now decreases the effective friction against which you can pull.
So even though your fingers/hands can still exert the same force, some of that force gets caught up in that sideways friction, thereby decreasing the overall pulling effort.
Zack explains this frictional force concept in greater detail:
Finding the ideal balance of frictional force
Of course, this analysis simplifies the situation, and there are often many reasons to separate your fingers. Perhaps you find a hidden little thumb catch that turns that crappy crimp into a slightly-less-crappy pinch. Or maybe you can only fit two fingers in that bomber pocket along the chossy rail. Or maybe there’s that one spot on the almost-perfect jug where the rock is just too damn sharp!
While we lose some force by separating the fingers, we presumably gain more force (or at least, more useful force) from whatever advantage the new finger or hand orientation provides (turning a crimp into a pinch, for instance).
Photo: Ashton Martin
These principles can explain why compression moves become increasingly effective as the hold angles more vertically. In compression moves, the hands (now assuming fingers are together and just considering the angle of the hand with the rock) apply a horizontal force.
The more vertical the rock, the more the compressive force will be applied perpendicularly to the surface, which will yield a stronger effective friction to help keep you up. If we apply force in a more sloped manner, we have less friction available, and a corresponding likelihood of slipping.
Learning to work with friction in rock climbing
As climbers, we are constantly assessing those tricky hand holds to find the best way to use them. While fingers are usually kept together, we develop an intuition for understanding how we can separate our fingers to achieve the most effective force for a given situation.
Zack Lepore was born and raised in Florida where climbing was pretty much limited to trees. Being a science geek from birth, he was always drawn to nature and its wondrous beauty. While studying biochemistry in Boston, he began rock climbing at the climbing wall in his college’s gym and immediately became addicted. After leaving Boston, he traveled westward and “accidentally” ended up in Steamboat Springs, Colorado where he now works as a baker. When not adventuring in Rockies or baking, Zack likes to read fantasy series, dystopian novels, and books on physics and chemistry.
