Biomechanics: Motion, Force, Mass & Inertia

• Biomechanics principles include understanding types of motion, forces, mass, and inertia.

Types of Motion

• Linear motion: movement in a straight line.
• Angular motion: rotation around an axis.
• General motion: a combination of linear and angular movements.

Force

• Defined as a push or pull acting on an object.
• Force is calculated as mass multiplied by acceleration (Force = mass x acceleration).
• Forces can alter an object's shape or motion.
• Forces operate in pairs, as stated in Newton's 3rd Law.
• Measured in Newtons (N).
• Types include friction, air/water resistance (drag), and gravity.

Mass

• Mass is the amount of matter in an object.
• Measured in kilograms (kg).
• Weight is the product of mass and gravity (Weight = mass x gravity).
• Inertia: the tendency of an object to resist changes in its state of motion.
• Objects with greater mass have greater inertia.

Torque

• Torque is a force that causes rotation.
• Torque is calculated as force multiplied by the moment arm (Torque = force x moment arm).
• Torque is produced by an eccentric force.

Distance and Displacement

• Distance: the total length of the path covered during movement.
• Displacement: the change in position, including direction, from start to finish.

Speed and Velocity

• Speed: the rate at which an object covers distance (Speed = distance/time).
• Velocity: the rate of change of displacement with direction (Velocity = displacement/time).

Linear Acceleration

• Linear acceleration: the rate of change in velocity.
• Zero acceleration indicates constant velocity or that the object is at rest.

Angular Motion

• Angular speed, velocity, and acceleration are analogous to linear motion but describe rotational movement.

Newton's Laws of Linear Motion

• 1st Law (Inertia): An object remains at rest or in uniform motion unless acted upon by an external, unbalanced force.
• 2nd Law (Acceleration): Acceleration is proportional to force and inversely proportional to mass (Force = mass x acceleration).
• 3rd Law (Action-Reaction): For every action, there is an equal and opposite reaction.

Momentum

• Momentum: the quantity of motion of a moving body
• Momentum is calculated as mass multiplied by velocity (Momentum = mass x velocity).

Summation of Momentum (Force Summation)

• Summation of Momentum: The coordinated use of multiple body parts to produce maximal force.
• Involves using many body parts, starting with large and slow to smaller and faster body parts.
• Sequential acceleration (timing) is essential for maximizing force.
• Requires stabilization of body parts to transfer momentum effectively.
• Follow-through is important for ensuring complete transfer of momentum.

Impulse

• Impulse: a change in momentum.
• Impulse is calculated as force multiplied by time (Impulse = force x time).
• Impulse can be used to either increase or decrease momentum.
• Increasing the time of force application reduces impact force while maintaining the same impulse (absorbing force).

Angular Momentum

• Angular momentum: the quantity of angular motion an object possesses.
• Angular momentum is calculated as moment of inertia multiplied by angular velocity (Angular momentum = moment of inertia x angular velocity).
• Moment of Inertia: A body’s resistance to rotation.
• Moment of inertia is calculated as mass multiplied by the square of the radius (Moment of inertia = mass x radius²).
• Moment of inertia is affected by mass distribution relative to the axis of rotation.

Conservation of Angular Momentum

• Conservation of Angular Momentum: Angular momentum remains constant in the absence of external torques.
• Changes in moment of inertia result in inverse changes in angular velocity (e.g., tucking or layout in gymnastics).

Levers and Mechanical Advantage

• Anatomical levers are third-class levers (axis-force-resistance).
• Mechanical advantage: force arm / resistance arm.
• Mechanical advantage in third-class levers is typically less than 1, which acts as "speed magnifier".
• Increasing the length of the resistance arm further decreases mechanical advantage but increases speed at the end.
• "Choking up" on a bat decreases the resistance arm, increases mechanical advantage (closer to 1), reduces swing speed but also the torque required, improving control.

Projectile Motion

• Projectile Motion: Factors affecting trajectory.
• Speed of release.
• Height of release.
• Angle of release.
• Manipulated based on the goal (accuracy or distance).

Equilibrium, Stability, and Balance

• Equilibrium: Balanced opposing forces.
• Types of equilibrium: static (at rest) and dynamic (constant velocity).
• Balance: Ability to control equilibrium.
• Stability: Resistance to changes in equilibrium.
• Factors increasing stability: increasing base of support, lowering center of gravity, keeping the line of gravity within the base of support, shifting the line of gravity towards oncoming force, extending the base of support towards oncoming force, increasing mass, and increasing friction.
• Decreasing factors reduces stability.