Chapter 2: Basic Biomechanics

Practice flashcards covering basic biomechanical principles, forces, Newton's laws, and simple machines from Lynn S. Lippert's Chapter 2.

Biomechanics

The application of mechanics to the human body.

Statics

One of the two main areas of mechanics, focusing on factors associated with non-moving systems.

Dynamics

One of the two main areas of mechanics, focusing on factors associated with moving systems.

Kinetics

Forces that produce stabilization or movement within a system.

Kinematics

Motion produced by forces, incorporating factors of time, space, and mass.

Scalar quantity

A measurement that has magnitude only, such as speed ($MPH$), length, area, volume, and mass ($lbs$, kilos).

Vector

A measurement that has both magnitude and direction, such as force, velocity, and acceleration.

Force

The amount of push or pull applied to objects or body segments; push creates compression while pull creates traction.

Internal forces

Forces including muscle contraction and ligamentous restraint.

External forces

Forces including gravity and any externally applied resistance.

Gravity

The mutual attraction between the earth and an object.

Gravitational force

The force exerted on an object or person by gravity.

Weight

The result of gravitational force and the mass of an object, always pushed directly downward.

Ground reaction force

The upward force a supporting surface exerts when an object pushes downward on it.

Friction

The force between two surfaces that increases resistance to motion of one surface across another.

Linear forces

Two or more forces acting along the same line.

Parallel forces

Forces that occur in the same plane and in the same or opposite direction.

Force couple

A specific configuration of parallel forces where two or more forces act in different directions to produce clockwise or counterclockwise rotation.

Concurrent forces

Two or more forces acting on an object pushing or pulling in different directions.

Resultant force vector

The sum of the magnitudes and directions of each individual force vector acting on an object.

Traction

An effect of force application where joint surfaces pull apart.

Compression

An effect of force application where joint surfaces push closer together.

Shear

A gliding motion of joint surfaces parallel to one another.

Bending

Force applied away from the central axis of an elongated object, causing compression on the concave side and traction on the convex side.

Torsion

Two opposing forces twisting within an object in opposite directions.

Torque ($T$)

The tendency of a force to produce rotation about an axis, calculated as $T = F \times MA$.

Moment arm ($MA$)

The perpendicular distance between the line of application of force and the axis of motion.

Newton’s First Law (Law of Inertia)

An object stays at rest or in motion at a constant state unless acted upon by an external force.

Newton’s Second Law (Law of Acceleration)

The acceleration ($a$) of an object is inversely related to its mass ($m$) and directly proportionate to the force ($F$) applied ($F = ma$).

Newton’s Third Law (Law of Action-Reaction)

For every action there is an equal and opposite reaction.

Equilibrium

When the sum of all forces acting on an object is equal to zero, resulting in no motion.

Center of mass ($COM$)

The point at which the sum of the mass of all body segments is located.

Center of gravity ($COG$)

The point at which gravity acts on the center of mass.

Base of support ($BOS$)

The areas encompassed by the body’s contact with the supporting surface.

Line of gravity ($LOG$)

An imaginary vertical line passing through the center of gravity toward the center of the earth.

Linear motion

Motion where all parts of an object move the same distance at the same time.

Curvilinear motion

Motion that occurs in a curved path that is not circular.

Angular motion

Movement of an object around a fixed point (axis) where all parts move through the same angle at the same time but not the same distance.

Simple machine

A tool that permits a change of effort ($F$) or direction of force required to lift a load.

Mechanical advantage

The relationship between the force expended and the load moved.

Lever

A rigid "plank" that rotates about a fulcrum (axis) when forces are applied.

Force arm ($FA$)

The moment arm between the axis and the force applied.

Resistance arm ($RA$)

The moment arm between the axis and the resistance (load).

First Class Lever

A lever where the axis is between the force and the resistance ($F-A-R$).

Second Class Lever

A lever where the resistance is between the axis and the force ($A-R-F$), meaning the force arm is always longer than the resistance arm.

Third Class Lever

A lever where the force is between the axis and the resistance ($A-F-R$), meaning the resistance arm is always longer than the force arm.

Pulley

A grooved wheel that turns about an axis with a rope, used to change the direction or magnitude of an applied force.

Fixed pulley

A single pulley attached to a fixed point that acts as a first class lever.

Movable pulley

A system combining a fixed pulley (to change direction) and a moving pulley to change the magnitude of force required to lift a load.

Inclined plane

A slanted surface (ramp) where less force is required over a greater distance; wheelchair ramps require a $1\text{ inch}$ rise for every $1\text{ foot}$ run.