Biomechanics terms

Force

Push or pull acting on body

Mass

Quantity of matter

Inertia

Resistance to action or change

Net force

Has magnitude and dircection, vector sum of all forces acting on a body

Linear system

Forces acting on body are all colinear, concurrent, coplanar

Nonlinear system

Forces acting on body are vertical and horizontal forces, hypotenuse is resultant force

Center of gravity/Mass

Point around which body is balanced, index for total body motion in analysis

Weight

Amount of gravitational force exerted on a body, weight= mass x acceleration of gravity

Pressure

Force over a given area, pressure= force/ acceleration

Volume

Amount of space an object occupies

Density

Mass per unit of volume

Specific weight

Weight/ unit of volume

Torque

Product of perpendicular force and distance from line of action to axis

Rotary force- Force applied not through the center of mass (apart of torque)

Impulse

Product of force and time, impulse= Force x torque

Compression

Squeezing force

Tension

Pulling force

Shear

Force vector parallel to the cross section

Mechanical stress

Distribution within a body (force/unit area), quantified as pressure

Bending

Nonaxial- compressive on one side and tensile on the other

Torsion

Twisting on longitudinal axis (one end of structure typically fixed)

Combined loading

Presence of one or more types of loading

Acceleration

rate at which velocity changes with time, in terms of both speed and direction.

Deformation

Change of shape

Failure

Loss of mechanical continuity (bone fracture, soft tissue rupture)

Acute

Single force large enough (macrotrauma) to cause injury

Repetitive

Relatively small force (microtrauma) continued over time

Biomechanics

Study of mechanics as it relates to anatomical analysis of biological systems

Mechanics

Study of physical actions of forces (static and dynamic)

Kinetics

The study of forces associated with the motion of a body

Kinematics

Description of motion and includes time, displacement, velocity, acceleration, and space factors of a system’s motion

Levers

A rigid bar that turns about an axis or fulcrum

Bones are the bars, joints, are the axis (most times), muscles contract to apply force

First class lever

Axis between force and resistance

Second class lever

Resistance between force and axis

Third class lever

Force between resistance and axis

Translation

All system parts move same direction same speed

Rectilinear

Along a straight line

Curvilinear

Along a curved line- no rotation

Angular motion

Rotation around an axis

General motion

Combined translation and rotation, most human movement is a general motion

Spatial reference

Plotted on Cartesian coordinate system, joints generally plotted, various capture devices