Foundations of Biomechanics III: Kinetics Flashcards Preview

DPT 726: Orthopaedic Foundations > Foundations of Biomechanics III: Kinetics > Flashcards

Flashcards in Foundations of Biomechanics III: Kinetics Deck (15)
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Definition of Force

-generally described as a push or pull
-exerted by one object on another
-precisely defined as F=ma
-therapeutic examples: gravity or weight of body parts and attachments, muscles, externally applied resistance, friction



-generally defined as anything require mental or physical effort
-more specifically: work=force x displacement



-rate of doing work



-a vector quantity secondary to magnitude and direction
-gravity=9.8 m/s^2
-line of action is always vertical
-direction is downward
-point of force on all points, but point of application given as center of gravity


Center of Gravity

-aka COM
-a hypothetical point at which all mass is equally distributed
-a point at which all mass would appear to be concentrated
-does not have to be in body


COG and Human Body

-slightly anterior to S2
-about 55% of person's height
-female's slightly lower
-infant's slightly higher


COG and Body Segments

-each segment has own COG
-location can change if segments combined


COG and Segmental Analysis

-if segment not equal in weight, COG is closer to heavier object
-if segments move, COG moves accordingly


COG and Stability/Motion

-height of COG above base of support
-AOTBE the lower the better
-App: athletes lower COG to improve leverage; therapists lower COG to do transfers
-size of BOS
-AOTBE increase stability if BOS widened in direction of line of force
-app: babies, elderly have wider gait to compensate for lesser strength and balance
-size of body
-AOTBE, increase stability with greater mass
-app: heavier individual better able to maintain equilibrium on offensive line
-line of force for multi-segmented body
-AOTBE, increased stability with COG for each body segment lines up in vertical line centered over BOS
-app: posture
-AOTBE, increase friction, increase stability
-app: non-skin shoes and surfaces
-increase in stability when focusing on stationary objects
-app: decrease visual disturbance with focal point


In what ways may PTs manipulate relationship between COG and stability/mobility?

-height of COG above BOS
-size of BOS (widen stance)
-size of body (harness above treadmill)
-line of force for multi-segmental body (align posture properly)
-friction and stability (sliding board)
-COG and maintaining balance


Newton's Third Law

-law of reaction
-force due to contact of two objects and their reaction to each other
-forces are: equal in magnitude, opposite in direction


Objects at Rest: Equilibrium

-body is in equilibrium when: at rest, moving at a constant velocity
-sum of all forces is equal
-exists until some other force acts on object causing it to: stop, start, or change motion
-Newton's first law
-law of inertia
-law of equilibrium
-D: object remains at rest or in uniform motion unless acted on by unbalanced force


Objects in Motion: Dynamics

-D: study of bodies that are accelerating or decelerating
-forces are unbalanced
-Newton's second law (law of acceleration or law of interaction)
-D: acceleration of an object is proportional to the unbalanced forces acting upon it and inversely proportional to the mass of that object
-F=ma, a=F/m


Clinical Applications

-body weight support is often used to decrease force of gravity: increase function, decrease pain or both
-PTs often increase or decrease load to optimize therapeutic stimulus: organism, task, and environment
-PTs often change movement patterns in order to decrease stress on area or facilitate healing


Take Home Points

-study of kinetics informs all aspects of PT practice
-work, power, and COG are central terms to describe motion of person's under care of PTs
-COG affected by many factors
-Newtonian mechanics allow us to quantify forces demonstrated by humans