Different snow conditions and temperatures create different magnitudes of friction. Te degree of friction is extremely low while skiing on ice on a relatively warm day, and high while skiing on the sharp, crystalline snow of a very cold day. When skiers hit a bare surface (no snow) during a spring thaw, the degree of friction is very high, usually causing them to decelerate abruptly, and perhaps pitch forward into a fall. In scientific terms, the force of friction is equal to the perpendicular component of force on the snow multiplied by the effect of friction.
CENTRIPETAL FORCE (LATERAL FORCE)
In a turn, centripetal force is the lateral (sideways) force from snow pushing against an edged ski. It is an inward force, toward the center of the turn and parallel to the surface of the snow. Tis lateral force is required for every type of turn. To address the basic physics of turning, the relatively tiny forces of friction and air resistance will be neglected. Similarly, discussion of forward inertia is not relevant. Ten, in a perfectly carved turn, where the ski is bent into a circular arc and the ski advances along that circular path without skidding, the only forces acting on the skier are the force of gravity and the force of the snow pressing against the ski. Te full force of the snow is distributed along the length of the ski and bends the ski into a circular arc. Te total force of the snow is represented by force vector S. Vector S can be resolved into two components: W and C. Component W is a vertical (upward) force, equal to the weight of the skier, exerted by the snow. Te second component, C, is directed toward the center of the turn. C represents the centripetal force, the sideways force that causes the skier to move along a circular path. Te skier exerts the force R on the snow that is equal and opposite to S. Te vertical component of R is the force of gravity, or the weight W. Te second component, ma,
PHOTO 3.7: Centripetal force is a lateral (sideways) force exerted by the snow on the ski during a turn.
ma R W C S W
TheSnowPros.org
CHAPTER 3: PHYSICS OF SKIING 53
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