Principles of Motion and Stability Chp.3

This set covers the fundamental principles of motor development, Newton's laws of motion, balance, stability, and the Carr’s 5-Step Process for skill analysis.

Kinematics

The description of motion, focusing on how an object is moving through position, velocity, and acceleration.

Kinetics

The study of the actions of forces, focusing on why an object is moving through concepts like force and moment.

Force

A concept used to describe the physical interaction of an object with its surroundings and an agent that produces a change in the state of rest or motion of an object.

Newton (N)

The unit of measurement for force, defined as $1\,N = (1\,kg) (1\,m/s^2)$.

Pound (lb)

The English unit for force, defined as $1\,lb = (1\,slug) (1\,ft/s^2)$.

Law of Inertia

Newton's first law stating that a body will remain at rest or continue to move with a constant speed in a straight line unless acted upon by an outside force.

Inertia

The resistance to change in motion, specifically a resistance to change in a body’s velocity, measured by an object’s mass.

Mass

The scalar quantity of the amount of matter in an object, which has a direct relationship with the resistance to change in motion.

Weight

A vector quantity representing the force due to gravity, acting downward with a magnitude of $9.81\,m/s^2$ times the body’s mass.

Law of Acceleration

Newton's second law describing the relationship where a force applied to a body causes an acceleration proportional to the force and inversely proportional to the body’s mass.

Law of Reaction

Newton's third law stating that for every active force, there is a second force equal in magnitude yet opposite in direction.

Kinetic Chain

The sequence of movements timed such that the mover applies the force of each succeeding movement just after the prior movement to accelerate the object.

Linear Velocity Formula

The calculation where linear velocity equals rotational velocity $\times$ radius of rotation.

Rotational Inertia

A measure of an object’s resistance to change in rotation.

Balance

The ability to maintain equilibrium.

Stability

The ability to resist movement.

Stability-Mobility Trade-Off

The inverse relation where movers initially maximize stability and balance, then shift to mobility strategies to move faster as they develop.

Carr’s 5-Step Process

A systematic method for observing and analyzing skill performance: 1. Observe complete skill, 2. Analyze phases, 3. Use mechanics knowledge, 4. Select errors, 5. Decide on correction methods.

Developmental Biomechanics

The study of the effects of forces on the musculoskeletal system during the entire life span.