Science Friction

the science of sticky

As a rock climber do you know how much environmental conditions can effect the amount of friction present between you and the rock?

Apprentice Level

understanding the basics of friction and optimizing your climbing conditions

The amount of friction generated is highly dependent on the two materials interacting, rubber on rubber has more friction then, rock on rubber, or skin or rock. Moisture in the form of sweat, rain, or condensation on the rock effects the way two materials interact and in almost all cases reduces the amount of possible friction, moisture also has the effect of softening the skin which makes it more pliable and prone to abrasion. When you as a climber use chalk it absorbs moisture from the skin, making the skin harder and increasing the amount of friction, it is not the chalk itself that helps, but the reduced moisture content. Besides chalk, you could use several other methods to reduce the amount of moisture present between the rock and your skin, antiperspirants, air dry (using a fan to dry the rock and hands), as well as planning the right time to climb to optimize the right conditions.

There are two main sources of moisture that will reduce friction while you are climbing, internal (from the body), and atmospheric.

Reducing the amount of internal moisture generated is a relatively simple concept, you simply find conditions (time of day) that are cool enough to climb in that you do not produce sweat. If temperatures are such that you are sweating here are some tips to reduce the sweat.

• reduce the amount of clothing you have on, climb as close to naked as possible, this will allow your body to radiate heat, which will reduce sweating

• find a shady spot you can rest between attempts

• carry a portable fan

Practitioner Level

understanding atmospheric forecast and conditions

The other source of moisture that will reduce the amount of friction is from the atmosphere. Atmospheric moisture is present in the air as water vapor, and when it shows up on the surface of objects is known as dew or frost. As rock climbers we are interested in the lowest amount of atmospheric moisture possible, this will make it easier for our body to evaporate sweat (more effective cooling for the body, as well as reduced moisture on the finger tips), and will reduce the amount of condensation possible on the rock (good for friction).

There are three things to pay attention to when considering atmospheric moisture content, the dew point and relative humidity and temperature. The temperature forecasted and its effects on climbing performance are easy to understand, the higher the temp them more sweat you will produce and the less friction you will have, but did you know that the amount of water vapor that can be present in the air is a function of air temperature, see the following graph, 77 degree Fahrenheit air can hold approximately 2.5 times that of 50 degree Fahrenheit air.

http://hyperphysics.phy-astr.gsu.edu

The amount of water vapor present in the air compared to what the air can hold at that temperature is referred to as the relative humidity, but if you examine the chart above you can see than at 77 degrees 50% humidity will be 2.5 times the moisture as 50% humidity at 50 degrees.

Which is where the third metric becomes very important, the dew point. The dew point is an indicator of how much water vapor is present in the atmosphere and as such is a more reliable indicator of water vapor present then relative humidity. At 15 degrees Fahrenheit with 100% humidity, there is 1/5 the water vapor present when compared to 50% humidity at 75 degrees Fahrenheit. The dew point in case A was 15 degrees, the dew point in case B was 50 degrees. At dew points above a 60 degrees it does not matter what the relative humidity is as there is so much moisture present that conditions will be poor for climbing. If you memorize the amount of water vapor that the air can hold at a specific temperature, and you know the relative humidity, you can work backwards to obtain the amount of water vapor present in the air, the simpler way is to look at the dew point and make a personal correlation between specific dew points and how you feel the friction is for the day. Bottom line dew point is measuring absolute humidity, whereas relative humidity is relative.

Wizard Level

The advanced trickery of dew points and temperatures

I mentioned earlier that dew or frost occurs when objects temperatures drop below the dew point, the converse is also true raise an object above the dew point and any moisture on the surface will evaporate, this is how sweat works in cooling our bodies (the human body is usually above the dew point temperature allowing sweat to evaporate off). For the best friction we want the temperature of the rock to be above the dew point, causing evaporation of moisture.

In the summer time late evening is often the best time for high friction as the rock will be above the dew point temperature still (having been heated in the sun all day), but will now be in the shade allowing for optimal climbing conditions. If you wait to long though the rock will begin to cool and you may end up with water vapor on the rock. Another useful trick is to look the forecasted dew point, sometimes it will drop off in the evenings which has the effect of drying things out, these drops in dew point are often accompanied by a wind which will be of extra help. Mornings often offer the advantage of cooler temperatures, but often the rocks will have dew on them, negating your advantage, want to climb well? Sleep in, hang out at the river all day, then go crush your projects as everyone else is retiring for the day.

In the winter time the best conditions often occur when the sun is still on the wall in mid afternoon. This is because in the winter time the amount of solar radiation is much lower then in summer time, so it takes a long time for the rock to heat up to be above the dew point. If you wait to long however the temperature of the rock will start to drop and your advantage will drop out. Dew points in the winter time are generally much lower when compared to summer time, so even if you ignore time of day and temperatures you will often end up with better conditions then in the summer (if you can handle the cold that is).

Sorcerer Level

its all irrelevant

Remember that although conditions do matter, what matters more is what you tell yourself when you are climbing. If you think the conditions will keep you from sending, they probably will. If you think that they probably have a negligible effect, that might also be true. Personally, I try to optimize for each given day that I climb, I worry less about scheduling which day, and instead only focus on what I can with what I have right now.