Biomechanics Definitions Flashcards
Kinetics
Study of relation existing forces acting on a body, mass of the body, and motion of the body
Kinematics
Describes motion without reference to force
Used to relate displacement, velocity, acceleration, time without reference to cause of the motion
Force
Vector quantity which produces or prevents motion
Imposes change of velocity on a material
Newton’s 1st Law of Motion
Every object in a state of uniform motion tends to remain in the state of motion unless external forces are applied to it
Newton’s 2nd Law of Motion
Relationship between object’s mass (m), acceleration (a), and the applied force (f), is given by the formula F=ma
Newton’s 3rd Law of Motion
Every action has an equal and opposite reaction
Equilibrium
State of object when no part of object is accelerating
Net force and torque acting on object is zero
Inertia
Reluctance of matter to change its state of rest or uniform motion
Fdeltat = mdeltavinitial- mdeltavfinal
3 Point pressure system
Principle in orthotic design to achieve joint stability
Provides point of pressure above axis of rotation, point below axis of rotation, and third opposing point at or near the axis of rotation
Moment
Measure of turning effect, or torque produced by force acting on a body
Equal to the product of force and perpendicular distance from its line of action to the point at which the body will turn (pivot)
Center of gravity and mass
Unique point in object or system which can be used to describe system’s response to external forces and torques
Average position of the system’s mass
Location in an object where mass balances in all planes
Force Couples
Moment induced by two equal and opposite forces
Is equal to the moment of one force about the point of action of the other
No resultant force
Lever, comprises of 3 components
Fulcrum
- point at which lever rotates
Load
- force applied by the lever system
Effort
- force applied by the user of the lever system
1st Class Lever
Fulcrum lies between effort and the load
2nd Class Lever
Fulcrum is at one end, effort on the other end, load lies between effort and fulcrum
3rd Class Lever
Fulcrum at one end, load at the other end, effort lies between load and fulcrum
Friction
Tangential force resisting motion of one surface on another
Work
Transfer of energy by force acting to displace a body
Product of force and distance
Kinetic Energy
Work done by force along a given displacement
Energy involved in motion
Potential Energy
Stored energy due to composition, position, or condition
Stability in Standing (2 conditions must be satisfied)
- Line of action of the TBF must be aligned within the base of support
- Joints must be stabilized by muscles, ligaments, etc.
Base of Support
Region bounded by body parts in contact with some resistive surface that exerts a reaction force against the body’s applied force
Usually feet or devices on the ground
But a hand on a railing or table also qualifies
Larger base of support, greater stability in standing
Medial-lateral body shift
Magnitude of GRF on each foot changes as the body shifts from its central position
Only evenly distributed among each foot if TBF is down the middle
Line of Action
Straight line extending along the direction of the force through the point of application
In static standing, the line of action of all the forces is purely vertical or in the y direction only
External Moment
Moment caused by a force outside the body in question
Active Internal Moment
Moments intentionally being created
Metabolic energy is used to create the moment
Muscle Contraction
Passive Internal Moment
Moments created without expenditure of metabolic energy
From ligaments, soft tissue, boney block (joint end range)
Moments caused by bracing can also be considered passive internal moments as long as the brace is within the segment being isolated
Ankle and Knee Moment most accurately predicted by
GRF
Hip Moment most accurately predicted by
TBF
Free Body Diagram
Diagram of isolated portion of structure used during free body analysis
For purpose of studying the effect of forces acting on the free body or body segment
Link Segment Model
Diagram that uses the line of action of the GRF/TBF to predict the moments that are occurring at a specific body joint
Momentum
Produce of mass and velocity
Quantity of motion of a moving body
Vector quantity, has direction and magnitude
Weight
Force that is the produce of the pull of gravity on a body’s mass
Always directed vertically downward toward the center of the earth
Earth pulling your body down by gravity is known as the total body force
Ground Reaction Force
The force exerted by the ground on a body in contact with it
Equal in magnitude and opposite in direction to the force that the body exerts on the ground
