Ski Bum Physics 101 – The Gravity Dance

Skiing is all about manipulating forces...

Gravity:

Gravity is the universal force that pulls two objects together. Here on this planet it's what makes us feel like we're stuck to the Earth's surface.

Obviously gravity is super important to skiing. When we stand on a slope covered in snow gravity is trying really hard to pull us towards the center of the earth. Fortunately the slope pushes back on us, and thanks to the slippery sticks on our feet, friction (another force that helps us stick) is reduced and we slide down the hill.

Now we've got some momentum!

Depending on how we manipulate our skis and align our body segments whille sliding, the snow pushes back on us to either slow our mass down, change it's direction, launch it into the air... or do a variety of other strange and wonderful things.

C.O.M. vs B.O.S.

Another important concept to understand in skiing is the relationship between the Centre of Mass and the Base of Support.

The Centre of Mass is the 3 dimensional balance point of an object. In a skier it's located somewhere just above the pelvis.

To make things more complicated, due to all our movable body parts, our Center of Mass actually moves around depending on what position we're in.

Move arm to one side... center of mass moves too!

Flex only at the ankles... COM moves forward

Bend only at the hips... center of mass moves forward

Flex both knees... COM moves back

The Base of Support refers to the area beneath an object or person that includes every point of contact that the object or person makes with the supporting surface.

In a skier this is the base of your skis and the area bewteen where they contact the snow. When you plant your pole this expands your base of support.

When we're just standing around without skis on, our base of support is the bottom of our feet.

Turning Forces:

Okay so we've created a steering angle by twisting our skis aganist our momentum... and we've tipped our skis on edge to get a little grip. Suddenly we start changing direction.

Centripidal Force helps us turn by pushing an object to towards the center of an arc.

Centrifugal Force (an apparently ficticious force) is caused by a constant change in momentum. It gives you that sensation of being pulled to the outside of an arc.

To balance while traveling on an arc, we need to find the happy place between gravity and centrifugal force.

This lean into the turn is called 'inclination.' The amount of inclination varies with speed and turn shape.

So why the physics lesson?

Well, if I were to sum up ski technique in one sentence, I would say we need to coordinate movements with all our different body parts so that our base of support, supports and directs our center of mass.

There you go... the secret to skiing!

Join the Science Friction Club.

You'll get to outsmart your ski instructor & troubleshoot your own ski technique.

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nancygreene
nancygreene
2 months ago

I live with two Physics teachers so this is what our dinner conversations sound like. Very interesting!

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