Foundations of Biomechanics III: Kinetics Flashcards
1
Q
Definition of Force
A
- generally described as a push or pull
- exerted by one object on another
- precisely defined as F=ma
- vector
- therapeutic examples: gravity or weight of body parts and attachments, muscles, externally applied resistance, friction
2
Q
Work
A
- generally defined as anything require mental or physical effort
- more specifically: work=force x displacement
3
Q
Power
A
- rate of doing work
- power=work/time
4
Q
Gravity
A
- 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
5
Q
Center of Gravity
A
- 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
6
Q
COG and Human Body
A
- slightly anterior to S2
- about 55% of person’s height
- female’s slightly lower
- infant’s slightly higher
7
Q
COG and Body Segments
A
- each segment has own COG
- location can change if segments combined
8
Q
COG and Segmental Analysis
A
- if segment not equal in weight, COG is closer to heavier object
- if segments move, COG moves accordingly
9
Q
COG and Stability/Motion
A
- 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
- friction
- 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
10
Q
In what ways may PTs manipulate relationship between COG and stability/mobility?
A
- 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
11
Q
Newton’s Third Law
A
- law of reaction
- force due to contact of two objects and their reaction to each other
- forces are: equal in magnitude, opposite in direction
12
Q
Objects at Rest: Equilibrium
A
- 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
13
Q
Objects in Motion: Dynamics
A
- 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
14
Q
Clinical Applications
A
- 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
15
Q
Take Home Points
A
- 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
