conditions of linear motion

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linear forces

2 muscle forces w/ same line of pull acting on the body is rare ex: gastroc+soelus iliacus+psoas major

rotary+stability

45*

rotary

90*

concurrent forces

acting @ the same point of application @ diff. angles results depend on force magnitudes+angle of application

gravity

always acts on an objects COG in a downward direction

muscle force

amount of force being produced is direct proportion to the number + size of contracting fibers

angle of pull

angle b/w bone and muscles insertion changes in angle pull will affect muscles ability to generate force on bony lever

magnitude

as long as force is greater than the the objects inertia, it will produce movement

pure rotation

balanced in opposite directions

linear

balanced in same direction

anatomical pulley

changes of muscles angle of pull ex. patella: increases angle of pull so rotary component increases for quad extension

direction

direction of force is along the action line, consider horizontal and vertical components

line of pull

direction of muscular force from insertion to origin

gravity

downward pulling force to center of the earth the closer you are to the surface=more gravity affects you

concurrent forces

force couples in the body. several muscles acting at the same time but in diff. directions affect a levers movement pull in diff. directions at the same time causing motion

linear forces

forces applied in opposit direction

linear forces

forces applied in the same direction along the ame action line = sum of forces -a+b =c ---------> + <------------------ = <---------------

parallel forces

forces not in the same action line but parallel to each other

destabilizing

gerater then 90*

force

has magnitude, direction, point of application

stability

less than 45*

weight

mass times acceleration due to gravity

muscle force

muscles act in groups strength is measured collectively MMT

parrallel forces

one force is stronger then the other, greater force applied to one side causes rotary motion

point of application

point where force is applied insertion site on bone - pt for muscular force

mass

substance an object is made of

direction

the closer the force is applied in the desired direction of motion, the more efficient the movement will be

linear with roation

unbalanced forces (one acting greater than the other)

parallel forces

unbalanced forces would produce linear motion (go upward)


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