Kinetics Flashcards
kinematics
displacement of a segment without regard to forces
Kinematic variables
-type
-location
-direction
-magnitude
-rate
Displacement Types
Translatory: linear movement (isolated force through COM), straight line, anterior drawer test
Rotary: angular movement (2 equal and opposite forces not through COM), center of rotation COR
General movement: translation + rotation (isolated force not through COM), curvilinear motion 2D, 3D
Movement Types (axis, plane, direction)
Flexion/Extension: Saggital plane, x-axis
Rotation: transverse plane, y-axis
Adduction/Abduction: frontal plane, z-axis
Force
-push or pull exert on on and object
-F=ma (N or lbs)
-must be touching
Gravity
-constant
g=9.8 m/sec^2
w=mg
-most consistent and influential force encountered by the body in posture and movement
Static Equilibrium
-object remains at rest
Dynamic Equilibrium
-object moves at a constant velocity
-constant acceleration= no equilibrium
Newton’s 1st law
-Law of Inertia: object in motion stays in motion until another force acts on it
-if net forces don’t = 0, movement must occur
-if only 1 force, cannot be equillibruim
Newton’s 2nd Law
-Law of acceleration: acceleration is directly proportional to unbalanced forces or torques and inversely related to mass or moment of inertia
-F=ma
-Linear a=F/m
-Angular a= torque/moment of I
Moment of Inertia
I=m(r^2)
-r=distance from axis of rotation
-dependent on mass and distribution of the mass
Linear force systems
-2 forces act on the same line
-sum of forces
Concurrent force systems
-2 forces act on different angles
-solve for parallelogram trig
Newton’s 3rd Law
-Law of reaction: equal and opposite reaction
-reaction forces
Tensile forces
-lengthening
-opposite pulls on the same object
-parallel to long axis of segment
Joint distraction forces
-directed away front the joint surface
-perpendicular to joint surface
Joint reaction forces
-when 2 segments are pushed together to touch
-compression force perpendicular to joint
Shear force
-action is parallel to contacting surface
-movement between surfaces
-same direction of movement
Friction force
-action is parallel to contacting surface
-opposite direction of movement
-static force is highest right before movement
Force Couple
-2 forces in equal magnitude in opposite directions
-always produce torque
Torque
T=(force)(movement arm)
-greater the force or distance between forces= greater torque
Movement Arm
-shortest perpendicular distance b/w forces
-from axis of rotation to force
Perpendicular force= Larger MA
Parallel force (most muscles)= smaller MA
Bending Moment
-3rd force applied to a force couple
-rotary equilibrium
Torsional Moment
-rotation along long axis
-twisting
Anatomical Pulleys
-change in direction of the pull of muscle by bony prominence
-makes task easier, increase movement arm= greater torque
Levers
-rigid segment that rotates around a fulcrum
-Effort force (EF) great that Resistance Force (RF) to produce rotation
1st Class Lever
-axis of rotation (fulcrum) between EF and RF
-scissors
-tilting head back and forth
OA joint= fulcrum
Trap=effort
Front of head= resistance
2nd Class Lever
-RF b/w fulcrum and EF
-wheel barrel
-Lifting heel off ground
Toes on ground= fulcrum
Calcaneus= resistance
Gastroc= effort
3rd Class Lever
-EF b/w fulcrum and RF
-shovel
-Flexing elbow
Elbow= fulcrum
Bicep attachment= effort
Wrist= resistance
Mechanical Advantage
-efficiency of the lever is determined by lengths of the lever arms
-MAd=EA (MA of effort force)/RA (MA of resistance force)
-EA>RA= MAd>1, requires less effort to move the lever
Force Resolution
Perpendicular: Fy, rotary
Parallel: Fx, translatory
-Pythagorean theorem
Angle of Application
-most angle of application muscles is small
-parallel component of a muscle force is usually larger than the perpendicular component
