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

Terms Kinematics: aspects of motion w/o consideration of mass and force Kinematics: aspects of motion w/o consideration of mass and force Kinetics: effects of forces upon motions of material bodies Kinetics: effects of forces upon motions of material bodies Energetics: energy and its transformations Energetics: energy and its transformations Motion: describes displacement, velocity and acceleration of a body in space Motion: describes displacement, velocity and acceleration of a body in space –Displacement: Δ in body’s position between locations –Velocity: rate of Δ in body’s displacement over time –Acceleration: rate of Δ in body’s velocity over time

Centrifugal: away from the center/axis Centrifugal: away from the center/axis Centripetal: toward the center/axis Centripetal: toward the center/axis Force: measure of the amount of effort applied Force: measure of the amount of effort applied –Internal force: applied by one part of body on another part of the same body –External force: applied by another object 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

Quadriceps force production throughout the ROM

Scientific Units of Measure Highlights Force (F): newton (N), some kg Force (F): newton (N), some kg –1kg=9.81N Work (w): distance + force; joule (J) Work (w): distance + force; joule (J) Velocity (v): km/h, m/min, m/s, °/s, rad/s Velocity (v): km/h, m/min, m/s, °/s, rad/s Power (P): watts (W) (force*distance)/time spent moving object Power (P): watts (W) (force*distance)/time spent moving object Energy (E): joule (J) Energy (E): joule (J) Boxes (p. 25) Boxes (p. 25) Table 2.4 (p. 26) Table 2.4 (p. 26)

Newton’s Laws 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. object must overcome inertia for movement to occur Formula: ___kg x 9.81 m/s 2 = ___ (force must be > than this to move) (Body wt in lbs / 2.2 = kg) i.e., 150#/2.2=68 kg 68 kg x 9.81 m/s 2 = 667.1N required to move 68 kg Factors influencing inertia: friction, air resistance Factors influencing inertia: friction, air resistance (e.g., base runner, skier)

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: Formula:F = ma Mass (in kg) m, acceleration a, and applied force F 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)

Momentum – –Product of mass & velocity –mass/velocity Δs –Changes as a function of mass/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

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

Energy and Power Kinetic energy: mechanical energy due to motion (joule, J) Kinetic energy: mechanical energy due to motion (joule, J) Potential energy: mechanical energy by virtue of height above ground (joule, J) Potential energy: mechanical energy by virtue of height above ground (joule, J) Elastic strain energy: stored energy in elastic tissues of muscles and tendons Elastic strain energy: stored energy in elastic tissues of muscles and tendons Power: rate of doing work (aka, strength x speed) (joule, J) Power: rate of doing work (aka, strength x speed) (joule, J) –Positive: concentric contractions produce energy –Negative: eccentric contractions absorb energy

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