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

segmental method of COM

determine COM of each segment then determine COM for several segments or whole body

center of gravity

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

line of gravity

plumb line

imaginary vertical line passing from COG of an object down to the ground

force vector of gravity

COG v COM

very similar but mass stays the same no matter what and gravity isn’t always consistent as radius changes BUT difference is VERY small

Center of Pressure

representative point of the force application

constrained to the area of “force application/contact”

where is COP regarding base of support

COP is within the BOS

relationship between COM and COP

travel in same direction

if one moves forward so does the other

what happens when line of gravity/COG moves OUTSIDE BOS

you fall

relationship between COM and LOG

travel in the same direction

between COG and COP which one moves more

COP to compensate for the COF changes and catch you

how to determine the stability of an object/body

location of LOG relative to BOS

size of the BOS(bigger is better)

distance between COM/COG and BOS(smaller is better)

weight of the object

friction between object and BOS(more friction = more stability)

move COG near expected force receiver side of BOS when anticipating a force

kinesthetic physiological functions

force of friction

force resisting the relative motion of 2 forces sliding against each other

opposite to the desired motion

can NEVER be more than desired motion force because that will pull it to the other side

=coefficient of friction * normal force

normal force

net force perpendicular to the surfaces

static v dynamic coefficient of friction

static is greater than dynamic

first class lever system

axis of rotation is in BETWEEN forces

MA depends on where the fulcrum is

Second class lever system

axis on one end

Resistance force is closer to AOR than effective force

greater advantage because effort arm is long(MA>1)

3rd class lever

AOR on one end

Effective force is closer to AOR than Resistance force

disadvantage bc MA<1(effort arm is shorter thar RA)

mechanical advantage

RF/EF = EA/RA

>1 = advantage

do less to move more

human muscles

most are 3rd class lever because of control and coordination while limiting power

limited number of 1st class

only 1 2nd class(if we go by the book)