Biomechanics: Levers and Vectors

mechanics

science of the effects of forces on matter

biomechanics

the application of the laws of mechanics to living structures, particularly regarding the interrelations of bones, muscles, and joints

kinesiology

study of muscles and muscle contraction; including factors affecting movement

kinematics

the study of possible motions of a system without regard to forces.

arthrokinematics

movements at the joint surfaces; roll, slide, spin, swing

osteokinematics

movements of the bones

kinetics

the study of relationships between the rate of change of a specific force, ie., gravity, surface friction, muscle contraction

statics

the equilibrium of bodies at rest

how do we move?

our nervous system signals muscles to contract which causes a bone to move around the axis of a joint

scalar

a physical quantity that has only magnitude, such as temperature, speed, and pressure

vector

a quantity possessing magnitude and direction

tensors

term for all quantities; zero, first, second order tensors

force

normal, tangential, tensile, compressive, shear, gravitational, friction

couple

a pair of equal and opposite parallel forces acting across a distance thus producing torque or moment

equilibrium

state where the net sum of all forces acting on an object equals zero. the object displays EITHER no movement OR a constant velocity.

stress

force per unit area of a structure and a measure of the intensity of that force. has magnitude and direction

strain

a measure of the degree of deformation of an object subjected to a load

translation

movement along an axis, x or y or z

torque

movement around an axis

lever systems

4 parts including a ridged beam, a fulcrum, a resistance, an effort

ridged beam

bones

fulcrum

joints

resistance

body mass, external load, gravity, inertia

effort

muscle workto move a load or resistance

first class levers

change the direction of the applied effort

second class levers

increase the force of the applied effort. (generally good at moving heavy objects)

third class levers

gain distance

resistance is between the fulcrum and the applied force

second class lever

applied effort is always between the fulcrum and the resistance

third class lever

mechanical advantage is always <1

third class lever

mechanical advantage is always >1

second class lever

second class lever

first class lever

third class lever

vectors

force having both magnitude and direction