Angular Motion: Physics Definitions

• Absolute Angle: Angular distance between a non-fixed segment and a fixed reference (e.g., Earth vertical).

Acceleration

• Average Acceleration: Change in velocity over a time period.
• Instantaneous Acceleration: Change in velocity at a specific instant.
• Angular Acceleration: Rate of change in angular velocity (vector quantity).

Angular Motion

• Angular Displacement: Change in angular position/orientation of a line segment.

• Angular Distance: Cumulative sum of all angular changes of a rotating body.

• Angular Impulse: Change in angular momentum, product of torque and time.

• Angular Momentum: Quantity of angular motion; product of moment of inertia and angular velocity.

• Definition: Rotation around a central line or point.

• Angular Speed: Rate of change in angular position/orientation (scalar quantity).

• Angular Velocity: Rate of change in angular position/displacement/orientation (vector quantity).

• Anthropometry: Study of body segment dimensions and weight.

• Applied Forces: Forces a body exerts on an object.

• Axis of Rotation: Imaginary line perpendicular to rotation plane, through the center.

Forces

• Bending Force: Asymmetric loading, tension on one side, compression on the other.

• Buoyant Force: Upward force of a fluid on a submerged body.

• Compression Force: Pressing/squeezing force axially through a body.

• Drag Forces: Resistive force opposite to motion in a fluid (skin friction, form, wave).

• Shear Force: Force directed parallel to a surface.

• Torsion Force: Twisting force around a body's longitudinal axis.

• Bio: The study of living things.

• Buoyancy: Ability/tendency to float.

• Center of Mass: Point where mass is balanced, regardless of position.

• Center of Gravity: Point where weight is balanced, regardless of position.

Friction

• Coefficient of Friction: Index of interaction between two surfaces (0 to 1).

• Static vs. Dynamic Friction: Dynamic is typically lower.

• Coefficient of Restitution (e): Index of elasticity for colliding bodies.

Fractures

• Comminuted Fracture: High-energy impact.
• Fissured Fracture: Direct trauma to a long or flat bone.

Material Properties

• Compliant Object: Shallow load deformation curve, much deformation from little force.

• Elastic: Returns to original length after deformation.

• Elastic Modulus: Normalized stress/strain curve equivalent in the elastic region.

• Stiffness: Slope of the load deformation curve.

• Conservation of Angular Momentum: Constant total angular momentum without unbalanced torque.

• Coordinate System: System using coordinates to define position.

• Cortical Bone: Compact, low-porosity bone in long bone shafts.

Motion

• Displacement: Change in location from origin in a straight line.

• Distance: Total path length traveled.

• Dynamics: Mechanics of systems undergoing acceleration.

• Energy: Capacity to do work (Joules).

• Ergometry: Measurement of work performed.

• External Forces: Forces acting on a system from outside.

• Failure Point: Point where a material breaks.

• Dynamic Flexibility: Range of motion during active movement.

• Static Flexibility: Range of motion during passive movement.

• Force: Push or pull, causes acceleration (F=ma).

• Force-Velocity Curve: Relationship between force and muscle action velocity.

• Formal Problems: Problems with a single answer.

• Free Body Diagram: Sketch of isolated system and forces acting on it.

• Friction: Force opposing motion at surface contact.

Laws

• Newton's 1st Law (Inertia): Body at constant motion unless acted upon by a force.

• Newton's 2nd Law (Momentum/Acceleration): F=ma, force causes change in momentum/acceleration.

• Newton's 3rd Law (Action-Reaction): Equal and opposite forces between two bodies in contact.

• Wolff's Law: Bone adapts to load, laid down where needed, reabsorbed where not needed.

• Ground Reaction Forces: ground force that acts upwards on a body.

• Impact: Collision with large force over a short time.

• Impulse: Product of force and time interval.

• Inertia: Resistance to change in motion.

Calculus

• Differentiation: Estimating curve slope (velocity from position change, acceleration from velocity change).

• Integration: Estimating area under a curve (velocity change from acceleration, position change from velocity).

• Internal Forces: Forces generated within a system (e.g., muscle force).

• Kinematics: Movement form, pattern, and sequencing with respect to time.

• Kinetic Energy: Energy of motion.

• Kinetics: Study of the action of forces.

Lever Systems

• Lever: Rigid object rotating around an axis, amplifies force or motion.
• Applied Force: Force applied to cause rotation
• Resistance Force: Force that opposes the applied force
• Line of Action of the Force: Imaginary line along which the force acts
• Mechanical Advantage: Applied moment arm / resistance moment arm. >1 implies strength advantage, <1 implies range of motion advantage.

Motion

• Linear Motion: Motion in a straight or curved line.

• Rectilinear: Motion in a straight line

• Curvilinear: Motion in a curved line

• Load: Force exerted on a surface or body.

• Mass: Quantity of matter, measure of inertia.

• Mechanics: Study of forces and their effects.

• Moment Arm: Perpendicular distance between force line of action and axis of rotation.

• Moment of Inertia: Resistance to angular acceleration, based on mass distribution.

• Momentum: Quantity of motion.

• Motor Unit: Motor neuron and innervated muscle fibers.

• Pennation Angle: Angle between muscle fibers and tendon in pennate muscles.

Math

• Pythagorean Theorem: a^2 + b^2 = c^2 (for right triangles).

• Quantitative Reasoning: Applying math skills to interpret quantitative data.

• Radian: Unit of angular measure (57.3 degrees).

• Radius of Gyration: Distance from axis to point where mass could be concentrated.

• Radius of Rotation: Distance from axis to a point on a rotating body.

• Physics: Study of matter, energy, and their properties.

• Physiological Cross Sectional Area: Muscle cross-section perpendicular to fibers.

• Plastic Region: Permanent deformation after force removal.

• Position: Location in space.

• Potential Energy: Energy of position (weight x height).

• Power: Rate of work production (W/time or FV, Joules/s).

• Pressure: Force per unit area.

Projectile Motion

• General Projectile: Free fall under gravity and air resistance.

• Classic Projectile: Take-off and landing heights are the same.

• Radial Acceleration: Acceleration towards the center of curvature.

• Relative Angle: Angle between two segments not fixed in space.

• Resistance Force: Force opposing applied force.

Hand Rules

• Right Hand Rule - Axes: Index finger = +x axis, middle finger = +y axis, thumb = +z axis.
• Right Hand Rule - Rotary Systems: Thumb = positive axis, fingers curl in direction of positive rotation.

Quantities

• Scalar: Defined only by magnitude.

• Vector: Defined by magnitude and direction.

• Slope of a Curve: Rise / run.

• SOHCAHTOA: Sine = Opposite/Hypotenuse, Cosine = Adjacent/Hypotenuse, Tangent = Opposite/Adjacent.

• Speed: Change in distance over time.

• Statics: Mechanics of systems at constant motion.

• Strain: Change in length / initial length.

• Strain Energy: Energy stored in an elastic body under load.

• Stress: Internal force per unit area (F/A).

• Systematic: Methodical, according to a plan.

Acceleration types

• Tangential Acceleration: Acceleration along the path of motion, represents linear speed change.

• Toe Region: Early part of load deformation curve, represents tissue tightening.

• Torque: Rotary effect of a force around an axis (force x moment arm, Nm).

• Trabecular Bone: Porous bone at long bone ends and vertebrae.

• Velocity: Displacement over time.

• Volume: Amount of 3D space occupied.

• Weight: Gravitational force on a body.

Curve areas

• Elastic Region: Returns to original shape after deformation.
• Plastic Region: Does not return to original shape after deformation.
• Yield Point: Transition between elastic and plastic regions.