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 forceUsed to relate displacement, velocity, acceleration, time without reference to cause of the motion
Force
Vector quantity which produces or prevents motionImposes 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 acceleratingNet force and torque acting on object is zero
Inertia
Reluctance of matter to change its state of rest or uniform motionFdeltat = mdeltavinitial- mdeltavfinal
3 Point pressure system
Principle in orthotic design to achieve joint stabilityProvides 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 bodyEqual 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 torquesAverage position of the system’s massLocation in an object where mass balances in all planes
Force Couples
Moment induced by two equal and opposite forcesIs equal to the moment of one force about the point of action of the otherNo resultant force
Lever, comprises of 3 components
Fulcrum- point at which lever rotatesLoad- force applied by the lever systemEffort- 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 bodyProduct of force and distance
Kinetic Energy
Work done by force along a given displacementEnergy 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 support2. 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 forceUsually feet or devices on the groundBut a hand on a railing or table also qualifiesLarger 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 positionOnly 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 applicationIn static standing, the line of action of all the forces is purely vertical or in the y direction only
