Transcript Introduction to Program Evaluation

Energetic Concepts
Dr. Suzan Ayers
Western Michigan University
(thanks to Amy Gyrkos)
Terms (Carr)
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Mass: matter, remains constant
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Weight: gravitational pull, varies with location
– You weigh < @ equator, > toward poles
2 characteristics of inertia (resistance to change) :
-to resist motion
-to persist in motion (in a straight line)
In linear movement, mass=inertia
Rotary inertia involves how mass is distributed
relative to axis of rotation
Factors influencing inertia: friction, air resistance
(e.g., base runner sliding, ski jumping)
Newton’s First Law
I. Law of Inertia
– Every object in a state of uniform motion tends to
remain in that state of motion unless an external
force is applied to it
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Speed: how fast an object moves
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Acceleration: an object’s rate of speed change
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Velocity: how fast & in what direction an object
moves
Momentum
– Product of mass & velocity
– Changes as a function of mass or velocity Δs
Velocity Δ: shot putter who spins faster one time vs
another
 Mass Δ: swinging a heavier bat

– Short stopping time requires ↑ force to Δ
momentum velocity
i.e., ‘giving’ when catching a ball or landing
 Key to injury prevention
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Conservation of momentum and energy:
http://www.walter-fendt.de/ph11e/ncradle.htm
Gravity’s effect on athletic performance

“Thin” air @ altitude: same proportion of gases,
but as altitude ↑, standard volume of air has <
of each gas (have to work harder to get same O2)
Acceleration of gravity

Uniform velocity of 32ft/sec: due to constant ↑
in velocity, increasingly large distance is
covered each sec. an athlete falls (Fig 2.1, p. 17)
Newton’s Second Law
II. Law of Acceleration
– Change of motion is proportionate to the force
impressed and is made in the direction of the
straight line in which that force is impressed
Objects accelerate in the direction pushed
Formula: F = ma
Applied force F, Mass m, acceleration a
Directly proportional (push 3x harder=3x> acceleration)
Inversely proportional to mass (object that is 3x heavier
moves 1/3 slower; bowling ball vs. volleyball)
If force or time ↑, so does velocity (i.e., keeping contact w/
ball longer = > time)
Center of gravity

Dead center (evenly distributed mass
(p. 21))
Gravity’s effect on flight

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Vertical & horizontal forces applied: flight path
cannot be changed once athlete is in flight
Ground reaction force: Earth’s push up on body
(Fig 2.7, p. 23)
Newton’s Third Law
III. Law of Action-Reaction
– Every action has an = and opposite reaction
Force: push/pull that changes shape or state of
motion of athlete or object
Vector: a quantity (of force) with direction
Force vector: when direction & amount of applied
force are known
Relevance? Vector analysis is learned by athletes
practicing various combinations of horizontal
and vertical pathways (lead passing routes, etc.)
Linear motion: straight line movement
(100m dash)
Angular motion: body moves through an angle or
number of degrees around an axis (360° dunk)
General motion: combination of linear/angular
Projectiles
Trajectory: flight path, influenced by gravity and
air resistance
Angle of release: influences shape of flight path;
1) straight up=vertical flight path
2) closer to vertical (+45°)=height > distance
3) closer to horizontal (-45°)=distance > height
Speed of release: apex of flight path ↑ as speed ↑
Height of release: relative to landing surface;
velocity (speed and direction), height and angle of
takeoff combine to determine flight path
Terms (Abernathy et al.)
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Energetics: energy and its transformations
Centripetal: toward the center/axis
Centrifugal: away from the center/axis
Moment of force: measure of the force needed
to rotate a body around a point
Equilibrium: all points of body have = velocity
– Static equilibrium: all points’ velocity/acceleration=0
Points of Application
1) Which muscles most important in the vertical jump?
 Quadriceps and gluteals
 SO WHAT?!
2) Relative to metabolic energy consumption…
 The cost associated with quiet standing is ~30% higher than
resting (sitting/lying down)
 SO WHAT?!
3) Walking saves met energy by converting gravitational
potential energy into forward kinetic energy. Running
stores/re-uses elastic strain energy, but less efficiently than
pendulum-like walking mechanism.
 SO WHAT?!
 Running less efficient than walking, ergo > caloric cost