riding from the snow up 2/10/02 - ron lemaster · 2010. 12. 9. · board and your line of motion...
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Riding From The Snow Up 2/10/02
Ron LeMaster © 2002 All rights reserved 1
Riding From
the Snow
Up
Ron LeMaster 2/10/02
The Text Book
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Riding From The Snow Up 2/10/02
Ron LeMaster © 2002 All rights reserved 2
My Approach
• Look carefully at the best skiers• Distill what is common• Seek an explanation for why it works
Technique and Methodology
• Technique– The movements that the athlete makes, as
described objectively by an external observer– This is not what you teach
• Methodology– The information presented to the athlete with
the intention of eliciting the desired behavior– Usually subjective in nature (kinesthetic, visual,
emotional)
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Riding From The Snow Up 2/10/02
Ron LeMaster © 2002 All rights reserved 3
The Rider’s Objective
• Control speed• Control direction• In other words, control velocity
Fundamental Mechanics
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Center of Mass
Hips and CM
• The CM is not usually in the rider’s hips
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Methodology and Technique
• Teaching method– “Keep your hips over your feet.”
• Technique– “Keep your center of gravity over your feet.”
Line of Motion
• The path followed by the skier’s CM• At every point in time, it points in the
direction of the skier’s momentum
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Riding From The Snow Up 2/10/02
Ron LeMaster © 2002 All rights reserved 6
Force
• A push or a pull• Something that causes a change in the motion of a
body• Has two parts
– Magnitude– Direction
• Force is related to pressure, but not the same thing• Is centrifugal force really a force?• Ski/snow friction causes linear deceleration only.
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How Things Turn
• The ball undergoes radial acceleration
• Where does the force come from?
The Snow Turns the Rider
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The Snow Turns the Rider
How a Board Carves an Arc
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Steering Angle
• The angle between the mid-body of the board and your line of motion
• To change your line of motion, the board must have a steering angle
• The board’s sidecut gives it built-in steering angles
Self-Steering Effect
• First, the board must turn. Then, you turn.
• The middle of the board makes you turn
• The tip and tail make the board turn
• The board cuts a groove in the snow like the inside of the bowl
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Sidecut vs Reverse Camber
How Can We Tighten the Arc?
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Inclination
Inclination
• Gravity and centrifugal force combine to form the resultant force on the rider
• The amount of inclination needed in a given turn is dictated by the direction of the resultant
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Inclination
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Inclination
• As newer equipment holds better, the rider must balance against larger forces, requiring– More inclination– Better physical conditioning
Gs - Resultant Force
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Gs - Resultant Force
Fundamental Movements
• How the rider affects the board’s control parameters– Up and down– Fore and aft– Edging– Pivoting– Balancing laterally
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Fundamental Movements
• The rider makes them to for different reasons
• Therefore, the rider should be able to make them independently
• The technically sophisticated and subtle rider can mix and match the movements to fit the situation.
Balance and Transition
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Balance
• There are two types of balance– Static– Dynamic– The terms are commonly misused by
instructors
• A boarder is rarely in static balance, and never in dynamic balance when riding
• Riding is like a broom balanced on your hand
Transition
• In a turn, the rider’s feet must follow a longer path than the CM
• Path of CM and path of feet must cross between turns
• Cross-over vs. cross-under– Difference is perceptual, not mechanical
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Transition
• The crucial move in snowboarding• The beginning snowboarder must learn
skills that advanced for a skier– Timing the moment of edge change– Controlled toppling– Estimation of anticipated force
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Transition Mechanics
• Board tightens its arc, so CM “falls to the outside”
• Feet and board slow down, e.g. via an edge-set, and CM topples across the feet
• By relaxing key muscles, upper body disengages from feet and its momentum carries it across
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Edgeset
Skis Tighten the Arc
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Flexion
Swapping Sides
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Methodology and Technique
• Teaching Method– “Project your center of mass down the hill.”
• Technique– “Put your body out of balance so your line of
motion crosses the path of your feet.”
The Virtual Bump
• Even on a smooth slope, turning creates a bump by– Going in and out of the
fall line– The path of the upper
body crossing over that of the feet
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The Virtual Bump
The Virtual Bump
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Redirecting the Board
Turning the Board
• Rotation– Board must be engaged in the snow, then
disengaged• Counter-rotation
– Board must be free of the snow• Differential slipping
– Pressure must be shifted toward one end of the board
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Rotation
Rotation and Counter-Rotation
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Thanks for Coming!