12 December 2008

Study found that having wet fingers does not reduce friction

An interesting study on how chalk and moisture affects a climber's grip was published in the Journal of Sports Sciences in 2001 [1]. The study found that applying water to the fingertips did not reduce friction. Their method involved pressing their fingers on a damp sponge. Shop clerks do this to give extra grip when they need to separate the layers of a plastic bag and people lick their fingers to make their fingers grip to the pages of a slippery magazine – does this mean that having wet hands increases grip for climbers? Any wet climbing experience will tell you otherwise. Climbers, weightlifters and gymnasts all use chalk to improve their grip, but with gymnasts they use it to allow their hands to slide more easily around the parallel poles. Clearly, the relationship between moisture, chalk and hand grip is not straightforward.

An extract from the study showing their experimental setup. From [1].

The authors attempted to tackle a very challenging subject for which it is difficult to create a meaningful experiment. How appropriate and how rigorous were their methods? “The fingers were pressed into a damp sponge … then pressed into a separate bowl of magnesium carbonate and the excess removed by tapping [the back of the hand]”. Is this representative of a real climbing scenario? How much chalk is applied? How much is removed by tapping? Is there anything in this method to prevent the following scenario? The fingers are wet from the sponge, and then they are dipped in just enough chalk to create a slimy paste on the finger tips.

They interpret their results as suggesting that “dry hands produce a higher coefficient of friction than when magnesium carbonate is applied to them. The effect would probably be amplified by the regular application of chalk, which desiccates the skin, reducing further the coefficient of friction.” And yet a few sentences later they state that “The manipulation of dampness did not yield any significant effect.” So dampness doesn’t affect friction, but if your hands are too dry it will reduce friction?

Furthermore, they conclude “All of this evidence strongly suggests that rock climbers should not use chalk when the fingers are already reasonably dry; if chalk is used to dry the hands, all traces of it should be removed before climing [sic]. As this is particularly difficult when rock climbing, an alternative method of drying the hands (e.g. using a towel) is preferable.” Their results show that having wet fingers does not affect friction – so why would they recommend drying your hands? They don’t believe their own results, if they have ever climbed before, this is not surprising.

[1] Journal of Sports Sciences, 2001, 19, 427-432. Pdf avaialable here:



Video Sol said...

The experiment could be improved if you do it inverted. Put hand straight and horizontal and then over the hand the rock with known mass, then rotate downwards the arm to increase the negative angle until rock slides. use that angle and the mass of the rock to calculate static friction coefficient. this way we eliminate errors caused by non constant forces created by the hand pressuring the rock below. sincerely: Albert Verdugo

Virgil said...

That sounds like an effective way of making the applied force consistent. I imagine that finding a way of applying chalk to the fingers which is consistent, and representative of how climbers use chalk, would be very difficult though.