Intro: Laws, levers, planes, axes Flashcards
Biomechanics
the application of classical mechanics to the analysis of biological and physiological systems
Axis and Coordinate Systems
Y is positive upward, X is positive anteriorly, Z is positive to the person’s right
Frontal Plane
formed by vertical (y) and mediolateral (z) axes; rotates about the anteroposterior (x) axis;
actions: A24, A44; lat bend
Sagittal Plane
formed by vertical (y) and anteroposterior (x) axes; rotates about mediolateral (z) axis
actions: flexion/extension
Transverse Plane
formed by the anteroposterior (x) and mediolateral (z) axes; rotates about the vertical (y) axis
actions: rotation
Kinematics
description of motion; displacement, velocity, acceleration, angular displacement/velocity/acceleration
Kinetics
description of forces; force and moment
External Forces
forces acting ON the body; force due to gravity, an external load, etc.
Internal Forces
forces acting INSIDE the body; could be a force produced by the muscle, passive constraint such as ligament or joint capsule
Moment Arm
perpendicular distance between line of action of the force and axis of rotation
Scalar Quantities
have direction only; can be positive or negative; add algebraically (only those with the same units); mass, distance, speed
Vector Quantities
have magnitude AND direction; usually noted with an arrow or underline; add by parallelogram method or law of cosines
Center of Mass
point at which the entire mass of an object can be considered to be located;
Base of Support and Stability
to increase stability, increase BOS area or move COM closer to the BOS
to decrease stability, decrease BOS area or move COM farther from the BOS
Center of Gravity
balance point for an object; location (given as coordinates)
Newton’s First Law: Law of Inertia
an object at rest will stay at rest, unless acted on by an unbalanced external force;
An object in motion will stay in motion unless acted on
Static equilibrium: sum of forces = 0
Newton’s Second Law: Law of Acceleration
acceleration is produced when a force acts on a mass (F=ma)
larger mass requires larger force to accelerate or decelerate
Newton’s Third Law: Law of Reaction
for every action there is an equal and opposite reaction;
reaction force acts in the opposite direction along the same line of action as the action force
Translational Motion
forces acting at one location; could be a colinear system (tug of war), concurrent force, or pulley force system
First Class Lever
“see-saw”; external force (load) and internal force (muscle) on opposite sides of fulcrum;
Ex: head
Second Class Lever
“wheelbarrow”; fulcrum and internal force (muscle) on opposite sides of the external force (load); MA muscle > MA external
Great mechanical advantage- can lift very heavy loads through short distances
Ex: toe raise
Third Class Levers
fulcrum and external force on opposite sides of the internal force; MAmuscle
