Understanding Friction Science | By Gil "Squeezus" Goodman
What if I told you that a simple technique tweak could deliver you through a whole hardstyle kettlebell certification weekend with little more than some skin soreness?
I was nearing the end of the second day of my StrongFirst SFG I Kettlebell Certification when I finished up a set of swings and looked around the room. We hadn’t even gotten to the snatch test and, out of around 40 athletes, only my partner Maria Bascetta and I were not sock-sleeving or taping our hands to cover or prevent blisters. Was it because we have superhumanly tough hand skin? Possibly...my application to the Avengers is still pending...but I also observed a key difference in chalk use between Maria and I and the rest of the room.
The majority of the athletes had sparingly and meticulously applied chalk to specific contact points on their hands and returned to the chalk bucket only once most of their chalk had sweated off. I chalked early, often, and thoroughly, covering the fronts sides and backs of my hands up to my wrists. It sounds simple, and it is but why would you chalk everything and not just the places you wanted to have grip?
On a rough, porous surface, like a stone, even a small amount of moisture can greatly reduce your friction. This is because the moisture acts as a lubricant between the microscopic protrusions from the porous surface and the ridges on your finger pads. By adding enough chalk to absorb the moisture (but not so much as to create a ball bearing effect with excess chalk), you are able to maximize your grip. This is “dry friction” which is most of us think of when we think of chalking it up. A small amount of moisture can sometimes help the chalk stick together and give a small boost to your friction, but in general, your friction will slowly taper off as the moisture content builds up.
Conversely, if you have ever tried to pick up a glass bottle (or something similarly smooth) with dry chalky hands, it was probably slippery. What about with dripping wet hands? Still slippery, right? But if your hands were just barely damp, they probably felt like they were glued to the bottle. This is because the moisture on your hands fills the microscopic gaps between your finger pads, via capillary force, and the glass to maximize the contact area and thus, your friction . The small margin of moisture greatly increases your grip, but a deviation in either direction and it drops off significantly. This is what we call “wet friction”.
So, what do wet and dry friction have to do with hand injuries during kettlebell training?
When you only chalk up specific points on your hand, you are:
- Allowing sweat from your arms and wrists to migrate to your hands more easily, and
- Creating a situation where you have dry friction where you chalked, which you can control by tightening or loosening your grip, and w et friction, which, because of capillary action, works independently of how hard you squeeze .
This means you could be trying to let the bell slide around loosely in your hand, but those wet friction spots are still sticking and pulling and creating hot spots and blisters. However, if you cover your entire hand with chalk, you have control over your friction and the frictional forces are more evenly distributed across your palm and fingers.
So, to recap:
- Chalk early. Don’t wait until the bell starts slipping around.
- Chalk thoroughly. Palms, fingers, back of hand, wrists, etc. It all sweats, and you don’t want that.
- Chalk often. It doesn’t last forever, so re-chalk before the bell start slipping around and causing hot spots.
Now, go ye forth and blister no more.
 Perlman, Howard. (2018). Capillary Action. U.S. Geological Survey. https://water.usgs.gov/edu/capillaryaction.html
 Fan, H & Gao, YX. (2002). Elastic solution for liquid-bridging-induced microscale contact. Journal of Applied Physics. 90. 5904 - 5910. 10.1063/1.1415057.