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sept 18 principles of motion chapt 3.doc

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University of Alberta
Physical Education and Sport
Jody Virr

Chapter 3 – Principles of Motion and Stability Overview • Principles of motion and stability that lead to proficient performance • Relationship between principles and motor behaviours characteristic of various skill levels Define: Biomechanics: the study of physics specifically applied to the body Developmental Biomechanics: What Changes From A to B? Beginner throwers have a jerky movement and they have more basic movement Advanced throwers have a transfer of momentum Changes Are Predictable • Based on optimizing principles of motion and stability • Can be seen across variety of motor skills • Often produce more force, velocity, or accuracy Newton’s First law • An object at rest stays at rest and an object in motion stays in motion until acted upon by a force • Inertia is resistance to motion related to mass • Momentum is the product of mass and velocity Newton’s First Law, Simplified We must exert force to • move objects • move ourselves More inertia means that • It is harder to move • More force application is required Newton’s First Law: Child Learns to Swing a Bat • What must the child learn about inertia? We have to consider the weight of the bat and the force required to slow down the swing of the bat • What must the child learn about momentum? Force to swing THE BAT AND THE ABILITY TO STOP THE BAT CERTAIN MOMENTUM IN THE RANGE OF MOTION Moving An Object farther Or Faster • Increase force • Increase distance over which force is applied • In a throw, adding a step increases the time in which are able to apply a move force • Applying a full ROM or rotational force, will increase the distant (full arm throw) • Muscles apply force, wither we increase force (strength) or the number of muscles recruited Adding Distance To Improve a Kick Increase step length (linear distance) Increase ROM (rotational distance) Newtons Second Law • Objects force is related to mass and acceleration ( F = m x a) • Objects acceleration is related to force applied and inversely related to mass • A person can only throw as hard as he or she can throw • Given a constant force level, how could you increase acceleration when throwing a ball? Newtons Third Law • To every action, there is an equal and opposite reaction • When you push on something, it pushes back on you • We have to take in account the object, force being applied ex. Sand or trampoline or sidewalk • When you push on something, it pushes back on you Using Newton’s Third law – Oppositional movements and directional force • To jump high, we are pushing down on the ground and backwards on the ground • In order to get the maximum force, we want to apply it over one plane • We want full extension of limbs • In running, we can absorb some of the force when our arms move up and down.. Force Generation Aided By Oppositional Movements Beginner runners run balanced because of their arms by their side Force Generation Aided by Planer Movements • Use force in the plane of motion where you want to move yourself or an object • Avoid rotational movements that reduce force in the desired plane Increasing Velocity: Rotating Limbs and Projected Objects • Increase rotational velocity (swing it faster): increase force applied. Increase ROM and to fully extend • Increase relative length (fully extend it at release or contact): we will be able to apply the force over a longer distance • To increase force, we want full extension, most possible number of muscles recruited Why not keep limb extended throughout? • The leg would have too much rotational inertia • More extension and wind up will increase the ROM • The shooting leg is bent because there is less force needed to pull it through • To produce the most force, we need it straight on contact • Ex. We can use this in basketball because the player must have
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