How Can Skiers Reduce Friction? (3 Key Forces)
When we ski the force of gravity acts down on our bodies and through our legs into the skis and the snow. Any source of friction will slow down our rate of progress and so skiers have learned to overcome these different forces.
Skiers can reduce friction before even putting on their skis. Properly prepared skis, which have had the bases prepared on a ski grinding and polishing machine will be much smoother than skis that are well used and scored. Skis are routinely waxed after grinding to create the smoothest finish possible. Waxing helps to reduce the friction between the ski base and the snow.
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3 Forces of Friction When Skiing
There are three forces of friction acting on any skier.
1. Static Friction When Skiing
Firstly, static friction is the force that keeps the skier at rest. When standing still on a run you may suddenly notice your skis break loose even though you’ve made no physical change. The coefficient of friction is greater than the kinetic friction, which stops you from moving.
Similarly, it is always difficult to push off on a flat surface from a standstill. Once you are moving the static friction is reduced and you need much less energy to keep propelling yourself forward.
2. Friction Between Your Ski & The Snow
Secondly, the friction that exists between the ski and the snow. As you ski down the slope your skis press against the snow. Newton’s third law of motion tells us that: ‘For every action, there is an equal and opposite reaction.’ This means the pressure you exert onto the snow with your ski is equaled by the same force of the hillside pushing back against you.
This is a strange concept to understand but it’s true. The equal opposing forces of your ski against the hillside and the hillside effectively pushing back create kinetic friction, which slows your progress down.
3. Friction from Air Resistance
Thirdly, all skiers are exposed to friction or drag from air resistance when skiing down a run.
As you ski your body parts the air in front of you, which uses the energy of your momentum, similarly behind you the air closes around your back creating a turbulent pattern, which additionally slows you down.
What is Kinetic Friction?
As you ski downhill your skis push against the snow creating kinetic friction, which in turn creates kinetic energy and subsequently thermal energy. This thermal energy is the heat that is released where your skis and snow are in contact.
The more friction, the more heat you generate instead of speed, and the slower you go forward.
Conversely, the more pressure that you put on your skis, the more pressure is applied to the snow underneath and the higher the likelihood that the snow will melt. Essentially skis slide because the layer of snow beneath the ski melts from your kinetic energy, which then creates thermal energy and melts a thin layer of snow.
The ski is then able to easily slide over this layer of water, which reduces friction. Afterward, the melted snow is free to refreeze as ice. You will notice on a run your ski is much freer to slide over the snow surface, this is because the energy can be transferred efficiently from your ski to the snow surface creating water to slide on.
However, in powder snow, energy transference from the ski to the loose powder is much less efficient, so less snow melts and the surface is less slippery.
Skis tend to follow the line of least resistance or friction. If you let go of a ski on a run it will tend to keep going in the same direction because that’s where there is the least resistance.
Similarly, if you ski forward with parallel skis, you will notice there is little resistance or friction. However, if you make a wedge turn (or Snow plough) as you are skiing down the same run you will feel the friction or resistance as the inner edges of the skis bite into the snow.
So, taking the most direct route down a run always minimizes the friction.
What Is The Tuck Position? & How Does it Help?
Putting your body into a tuck position will reduce wind resistance considerably. Friction and drag can also be reduced by wearing a ski jacket and ski pants that fit well.
There is a compromise between clothing that is so tight that it restricts your movements against clothes that are too loose, so they catch the air and slow you down. When skiing friction is created when you ski from side to side.
The energy which could have been used to get you down the run faster is instead used in pushing snow out of the way during a turn. So, the most direct route down the run will always have the least friction.
Skiers can also reduce friction by changing their body posture. Squatting down on your haunches or going into a tuck reduces the body’s surface area considerably. Having an effective tuck position makes a very big difference to wind resistance, and consequently, speed.
You can test this for yourself when you’re skiing on a flattish run. By just putting your arms and poles behind your back you will notice you speed up because your wind resistance was lowered.
How can you reduce friction between the Skis and the Snow?
As you pick up speed skiing down a slope you will build up kinetic energy, which is created from the act of moving and pushing downhill. The friction between the base of your ski and the snow will create thermal energy in just the same way as your hands become hot when you rub them together fast.
This thermal energy is wasted in skiing, as you are generating heat, but this does nothing to increase your speed.
This is where waxing the bases of your skis comes in very useful. The bases of skis are generally made from polyethylene and graphite, often under the trade name of P-Tex. This is a strong, porous material that offers low friction.
Protecting Ski Surface from Excessive Friction
All skis and snowboards will gradually become slightly scored on the base of the ski however careful you are to protect them. Ski rental shops often have the facility to regrind the bases and take them back to a new condition.
The process involves firstly regrinding the edges of the ski to ensure they are sharp. The skis or snowboards are then fed through the grinding machine, which has a stone wheel, which removes a very thin layer of the ski surface.
Waxing Skis To Slide Easier
The final part of the grinding is to re-wax the ski. Melted ski wax is poured onto the base of the ski and a hot iron is used to spread the wax in a very thin layer all over the base of the ski.
This is allowed to cool and set completely. A steel or polycarbonate ski scraper can then be used to remove the excess wax from the base of the ski before using a brush to buff the surface.
For most applications, hydrocarbon wax is best and slightly cheaper, while fluorocarbon waxes are more expensive and often used in professional skiing applications. There is a whole range of different waxes which are suited to different conditions of temperature and snow. The wax has three different functions:
- It lubricates the ski to make it glide over the snow better
- It reduces wear by providing protection from abrasion by ice and stones
- It acts as a barrier to stop water penetrating other layers of the ski
How What You Wear on The Slopes Changes Air Resistance
Ski clothing nowadays is often made from strong and durable man-made fibres. When choosing the fit for a ski jacket and ski pants it is best to go slightly larger because often you will be wearing extra layers underneath for warmth.
You need to have good freedom of movement to move your arms and legs as you assume different positions during skiing. However, you don’t want such a large fit that your wind resistance is increased too much.
There are numerous ways to reduce ski friction, some involve changes to clothing and equipment, and others involve different behavior and postures on the runs.
Friction isn’t your enemy
The idea of removing friction completely when skiing initially seems like a fun idea. Getting up to fantastic speeds in no time at all but of course, when you need to slow down, you’re stuffed. So, friction isn’t always something to be eliminated. Maintaining good control as you negotiate any snow surface should be a vital part of your skills.
You make use of the friction between the edges of your skis and the snow during turns. The kinetic energy of the speed you have built up is transferred through your legs into the ski edges, which bite into the snow surface slowing you down.
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