Kinetics of Human Movement

kinetics

actions of forces in producing or changing the motion of masses

force

push or pull that produces, arrests or modifies motion

characteristics of force

magnitude(length)

point of application(tail)

line of application(angle)

external forces

contact and non-contact forces

contact forces

ground reaction force, friction, fluid force, intertial force

non-contact force

gravity, magnetic force

internal forces

active, passive, bone-on-bone force contact/reaction force(Wolf’s law)

active internal force

musculotendinous unit(muscle force)

passive internal force

ligaments, fascia (tension under stretch)

newtons 1st law

an object in motion stays in motion and an object at rest stays at rest unless acted upon by an external force

netwon’s 2nd law

F= ma

Newton’s 3rd law

for every action there is an equal and opposite reaction

rotatory motion

created by torque

Torque

tendency of a force vector to rotate an object about some axis

T = F*LA

Lever arm

Perpendicular distance from axis of rotation to the line of applied force

longer lever arm = more torque

center of mass

hypothetical point where all of the mass of the system could be considered to be located

may be located out side of the system

how push a ball translationally but not rotatory

push directly through the center = no lever arm = no torque

calculating COM

sum of mass * position/ total mass of x coordinate

sum of mass * position/ total mass of y coordinate