Chapter 6 Linear Kinetics Explaining the Causes of

Chapter 6 Linear Kinetics Explaining the Causes of Linear Motion

Review Newton’s ? ? Laws of Motion

Newton I: Law of Inertia A body will maintain its current state of motion unless acted on by an unbalanced external force • External forces include airresistance and friction • Examples • passenger in car • projectile motion (horizontal)

Newton II: Law of Acceleration F = ma • A force applied to a body causes an acceleration of the body of a magnitude proportional to the force, in the direction of the force, and inversely proportional to the body mass • Example, kicking a soccer ball • At an instant in time

Newton III: Law of Reaction • For every action there is an equal and opposite reaction (forces act in mirrored pairs) • Ground reaction forces

How measurement has changed.

Current state of motion • How fast and in what direction • velocity: a vector quantity • How resistant to changing state of motion • inertia: quantified by mass Momentum: mass x velocity Momentum = mv

Momentum • Newton I: Law of inertia • Principal of Conservation of Momentum • In the absence of external forces, the total momentum of a given system remains constant

Momentum Example (15 July 1999, Alabama) A 25 -year-old soldier died of injuries sustained from a 3 -story fall, precipitated by his attempt to spit farther than his buddy. His plan was to hurl himself towards a metal guardrail while expectorating, in order to add momentum to his saliva. In a tragic miscalculation, his momentum carried him right over the railing, which he caught hold of for a few moments before his grip slipped, sending him plummeting 24 feet to the cement below. The military specialist had a blood alcohol content of 0. 14%, impairing his judgment and paving the way for his opportunity to win a Darwin Award.

Newton II: Law of Acceleration F = ma Develop the impulse-momentum relationship from this equation

Impulse to increase momentum and decrease momentum • Mechanical objective of human performance • move at a particular speed in a particular direction • ===> momentum • Alter perfomance (momentum) • force: magnitude, direction, point of application, line of action • time: duration of force application

Vertical jump • Jump • increase momentum to some high value • rest to upward motion • Certain impulse is required • m (vv - vi) • Alter time of force application • short time, large force • long time, small force

Soft and stiff landings • Landing • decrease momentum to Zero • downward motion to rest • Certain impulse is required • m (vv - vi) same with landing from a height • Alter time of force application • short time, large force • long time, small force

Child is uninjured because: 1) soft ground and leaves increase time over which child stops Effect on Force? ? ?

Homework Assignment • Due one week from today • unless otherwise stated • Review Questions Chapter 6 • pages 111 -112

Role of Movement Analyst Bob Norman (1976) & Shirl Hoffman (1977) • Recognize symptoms of malperformance • Is performance acceptable? Is the goal attained? • Process vs Product • Trouble-shoot the cause of the malperformance • Critical ability lacking • Skill performance deficiency • Psychosocial problem • Prescribe cues to correct malperformance • Make the appropriate intervention

Critical ability lacking Mismatch between the individual & the environment Modify the environment

Adapt the environment to the individual to enhance chances of success.

Psychosocial problems.

Psychosocial problems. I joined a health club last year, spent about $400. Haven’t lost a pound. Apparently, you have to show up.

Psychosocial problems.

Skill Performance Deficiency • Mechanical objective of a skill • momentum in particular direction(s)

Bob Norman (1976) • Mechanical objective of a skill • Idiosyncracy • individual nuance of performance that has no direct influence on mechanics of performance • Michael Jordan • batting stance

Unwarranted focus on static position of batting stance

So prove it. Physics is not the only science important in the game of baseball; it’s also a game of psychology, of pitchers trying to stare down batters, and batters trying to intimidate pitchers. And no matter what you tell me, I don’t believe that some guy standing in the batter’s box with his bat dangling loosely from his hands has nearly as much power as a guy snarling and gripping the bat hard, waving it menacingly over his head. It may be good science, but I’ll bet the second guy gets more hits. Suzanne Sparacino, Commack NY Letter to the editor, Discover magazine.

Bob Norman (1976) • Mechanical objective of a skill • Idiosyncracy • Symptom of an error • what we see go wrong (kinematics) • • not high enough not fast enough wrong direction body positions

Swing Level? Paul Popovich March 29, 1993.

Say what you mean.

Follow through Symptom or Cause? Game-winning shot vs Utah Jazz 19**? ? ?

Lead with the elbow

Shoulder External Rotation: Symptom or Cause of Great Performance?

Bob Norman (1976) • • Mechanical objective of a skill Idiosyncracy Symptom of an error Cause of an error • the underlying reason for the poor performance • mechanically: error in impulse application

Mechanical Phases of skill performance • Ritual Phase • Full of idiosyncrasies, useful for mental focus • Preparation • Wind up • Storage of elastic energy, increase ROM (Benefits? ) • Execution • Acceleration • Apply impulse to the body in the desired direction • Follow through • Bring moving parts to rest • Safety, symptom of good performance

Volleyball Underhand Serve Peer Rating Evaluation Sheet from a middle school session at IAHPERD conference 1. 2. 3. 4. 5. 6. 7. 8. 9. Is the arm which is holding the ball across the front of the body? Is the ball held at or below the waist? Is the body bent at the waist before the person hits the ball? Is the striking arm brought back with a straight elbow? Is the ball hit from a short toss or out of the hand? Does the hitting arm swing from the shoulder? Does the hitting arm swing straight, not across the body? Is the person stepping or standing with opposition? Is there a weight shift from the rear foot to the front foot when the ball is hit? 10. Does the striking hand follow through at least as high as the head after the ball is hit?

Possible reasons for elderly to walk slower • Not willing to walk faster • • • Wise enough to know that walking faster changes nothing Careful stepping due to slowing of reflexes Cautious Afraid of road hazards Afraid of falls due to OP, other catastrophes • Not able to walk faster • • • Reduced ability to maintain dynamic balance Reduced ROMs Reduced contents of fast-twitch muscle fiber Joint or muscle pathologies Reduce CV fitness

Long Lies • Phenom • Individual cannot rise from the ground • After a fall • Gardening • Housecare • Why not? List possible reasons, according to the Hoffman Checklist • Importance: Develop an intervention for prevention • Strength training? • Flexibility training? • Technique Training • What technique? Old vs Young? Healthy vs Infirm?

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