Biomechanics and Motion Fundamentals

Biomechanics

Study of structure and function of biological systems using mechanics methods.

Kinematics

Form, pattern, or sequencing of movement with respect to time; description of motion.

Kinetics

Study of the action of forces; cause of motion.

The Mechanical System

A body or portion of a body deliberately chosen to be analyzed.

Center of Mass (COM)

Point around which a body's mass is equally balanced; index of whole-body motion.

Center of Gravity

Effectively equals COM on Earth assuming gravity acts uniformly on the system.

Balance

Ability to maintain the body's center of gravity over its base of support.

Stability

Ability to return to a desired position or trajectory following a disturbance.

Motion

Changing place or position relative to a reference object, requiring space and time.

Linear Motion

Occurs when a system moves the same distance, direction, and time.

Rectilinear Motion

Straight line translation with no change in direction or orientation.

Curvilinear Motion

Curved translation where direction constantly changes without orientation change.

Angular Motion

Objects or body parts move in circles about a fixed central line or axis.

Circular Motion

Special curvilinear motion moving along a circle's circumference of constant radius.

General Motion

Combination of linear and angular motions, also called mixed motion.

Physical Quantity

Characteristic or property of an object that can be measured or calculated.

Unit

Standard for expressing and comparing measurements of physical quantities.

Base Units

Fundamental physical quantities defined only by their measurement procedure.

Derived Units

Algebraic combinations of base units expressing other physical quantities.

Linear Kinematics

Branch of dynamics concerned with the description of linear motion.

Scalar Quantity

Mathematical representation defined only by its magnitude.

Vector Quantity

Mathematical representation defined by magnitude and direction.

Position

Linear location of an object of interest at a given instant.

Distance

Measure of the length of the path followed from starting to ending position.

Displacement

Straight-line distance in a specific direction from initial to final position.

Speed

Rate of distance traveled; how fast an object moves.

Velocity

Rate of displacement and rate of change in position in a specific direction.

Acceleration

Rate of change in velocity caused by change in magnitude or direction.

Positive Acceleration

Speeding up of positive velocity, or slowing down of negative velocity.

Negative Acceleration

Slowing down of positive velocity, or speeding up of negative velocity.

Uniform Acceleration

Constant object acceleration occurring when net external force is unchanging.

Projectile

Object projected through air or dropped, acted on only by gravity and air resistance.