Linear Kinetics Explaining the Causes of Linear Motion

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Chapter 6

• Linear Kinetics Explaining the Causes of Linear
  Motion

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Review Newtons ???? Laws of Motion
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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 air-resistance and
  friction
• Examples
• passenger in car
• projectile motion (horizontal)

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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

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Newton III Law of Reaction

• For every action there is an equal and opposite
  reaction (forces act in mirrored pairs)
• Ground reaction forces

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How measurement has changed.
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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
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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

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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.
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Newton II Law of Acceleration

• ?F ma

Develop the impulse-momentum relationship from
this equation
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Impulse to increase momentum and decrease
momentum

• Mechanical objective of human performance
• move at a particular speed in a particular
  direction
• gt momentum
• Alter perfomance (momentum)
• force magnitude, direction, point of
  application, line of action
• time duration of force application

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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

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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

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

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

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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

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Critical ability lacking
Mismatch between the individual the
environment Modify the environment
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Adapt the environment to the individual to
enhance chances of success.
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Psychosocial problems.
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Psychosocial problems.
I joined a health club last year, spent about
400. Havent lost a pound. Apparently, you
have to show up.
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Psychosocial problems.
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Skill Performance Deficiency

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

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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

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Unwarranted focus on static position of
batting stance
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So prove it.
Physics is not the only science important in the
game of baseball its 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 dont believe that
some guy standing in the batters 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 Ill bet the second guy
gets more hits.
Suzanne Sparacino, Commack NY Letter to the
editor, Discover magazine.
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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

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Swing Level?
Paul Popovich March 29, 1993.
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Say what you mean.
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Followthrough
Symptom or Cause?
Game-winning shot vs Utah Jazz 19???
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Lead with the elbow
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Shoulder External Rotation Symptom or Cause of
Great Performance?
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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

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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

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Volleyball Underhand ServePeer Rating Evaluation
Sheetfrom a middle school session at IAHPERD
conference

1. Is the arm which is holding the ball across the
   front of the body?
2. Is the ball held at or below the waist?
3. Is the body bent at the waist before the person
   hits the ball?
4. Is the striking arm brought back with a straight
   elbow?
5. Is the ball hit from a short toss or out of the
   hand?
6. Does the hitting arm swing from the shoulder?
7. Does the hitting arm swing straight, not across
   the body?
8. Is the person stepping or standing with
   opposition?
9. 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?

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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

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Long Lies

• Phenomenom
• 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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