conditions of linear motion
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)