Energetic Concepts Dr. Suzan Ayers Western Michigan University (thanks to Amy Gyrkos)

Terms (Carr) Mass: matter, remains constant Mass: matter, remains constant Weight: gravitational pull, varies with location Weight: gravitational pull, varies with location –You weigh 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

Speed: how fast an object moves Speed: how fast an object moves Acceleration: an object’s rate of speed change Acceleration: an object’s rate of speed change Velocity: how fast & in what direction an object moves Velocity: how fast & in what direction an object moves

Momentum – –Product of mass & velocity –mass or velocity Δs –Changes as a function of mass or velocity Δs Velocity Δ: shot putter who spins faster one time vs another Velocity Δ: shot putter who spins faster one time vs another Mass Δ: swinging a heavier bat Mass Δ: swinging a heavier bat – Δ momentum velocity –Short stopping time requires ↑ force to Δ momentum velocity i.e., ‘giving’ when catching a ball or landing Key to injury prevention Conservation of momentum and energy:

Gravity’s effect on athletic performance “Thin” altitude: same proportion of gases, but as altitude ↑, standard volume of air has < of each gas (have to work harder to get same O 2 ) “Thin” altitude: same proportion of gases, but as altitude ↑, standard volume of air has < of each gas (have to work harder to get same O 2 ) 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) 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)

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 Newton’s Second Law

Formula: 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) ) Dead center (evenly distributed mass (p. 21) ) Gravity’s effect on flight Vertical & horizontal forces applied: flight path cannot be changed once athlete is in flight 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) Ground reaction force: Earth’s push up on body (Fig 2.7, p. 23)

III. Law of Action-Reaction – –Every action has an = and opposite reaction Newton’s Third Law

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

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 Projectiles

Energetics: energy and its transformations Energetics: energy and its transformations Centripetal: toward the center/axis Centripetal: toward the center/axis Centrifugal: away from the center/axis Centrifugal: away from the center/axis Moment of force: measure of the force needed to rotate a body around a point Moment of force: measure of the force needed to rotate a body around a point Equilibrium: all points of body have = velocity Equilibrium: all points of body have = velocity –Static equilibrium: all points’ velocity/acceleration=0 Terms (Abernathy et al.)

Points of Application 1) Which muscles most important in the vertical jump? Quadriceps and gluteals Quadriceps and gluteals SO WHAT?! SO WHAT?! 2) Relative to metabolic energy consumption… The cost associated with quiet standing is ~30% higher than resting (sitting/lying down) The cost associated with quiet standing is ~30% higher than resting (sitting/lying down) SO WHAT?! 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?! SO WHAT?! Running less efficient than walking, ergo > caloric cost Running less efficient than walking, ergo > caloric cost