Year 12 PE Studies Notes - Biomechanics

Linear Kinetics

  • Linear Momentum

  • Defined as the product of an object’s mass multiplied by its velocity.

  • Formula: P = m.v

    • P = Linear Momentum
    • m = Mass
    • v = Velocity

  • Linear Motion

  • Describes movement in a straight line.

  • Momentum increases with either an increase in mass or velocity.

  • Examples

  • Elephant Example:

    • Mass: 5000kg
    • Velocity: 10m/s
    • Linear Momentum = 50,000 kg/m/s

  • Cheetah Example:

    • Mass: 50kg
    • Velocity: 30m/s
    • Linear Momentum = 1500 kg/m/s

  • Application in Sports:

  • In Rugby, players use varying momentum to dodge or tackle opponents.

Impulse

  • Definition:

  • Change in momentum (∆p).

  • Formula:

  • Impulse (Ap) = F.t

    • Where F = Force, t = Time

  • Relation to Newton's Second Law:

  • Force = Mass x Acceleration

  • Impulse can be expressed as Force x Time

  • Force Production:

  • Example in Shot Put:

    • Impulse is maximized by increasing the time over which force is applied.

  • Force Absorption:

  • When absorbing force (e.g., catching a ball), increasing time reduces peak force.

Coefficient of Restitution (CoR)

  • Definition:

  • Ratio of the velocity after an impact compared to before the impact, representing the bounciness of an object.

  • Coefficients:

  • Perfectly Elastic Collision (CoR = 1): All energy is conserved.

  • Partially Inelastic Collision (0 < CoR < 1): Some energy is lost.

  • Perfectly Inelastic Collision (CoR = 0): No energy remains after the bounce.

  • Factors Affecting CoR:

  • Equipment and surfaces (new materials typically have higher CoR)

  • Velocity of collision (higher velocity reduces CoR)

  • Temperature (increased temperature typically increases CoR)

Angular Kinetics

  • Moment of Inertia (MoI):

  • Tendency of a body to resist angular motion.

  • Formula: I = ∑ mass * r²

    • Where r = distance from mass to the axis of rotation.

  • Lower MoI means it is easier to rotate the object.

  • Angular Momentum:

  • Quantity of rotation of a body given by L = ω.I

    • Where ω = angular velocity.

  • Angular velocity and moment of inertia are inversely proportional.

  • Third Class Levers:

  • Force is between load and fulcrum, promoting speed at the endpoint.

  • Example: Baseball bat, where maximizing leverage increases speed.

Biomechanical Principles

  1. Balance:
  • Ability to maintain equilibrium, influenced by base of support, height of center of gravity, line of center of gravity, and mass.
  1. Summation of Forces:
  • Coordinated use of body segments to produce force, either simultaneously or sequentially.
  1. Optimal Projection:
  • Relation between angle, velocity, and height of release to maximize performance.

Fluid Mechanics

  • Definitions:

  • Laminar Flow: Fluid travels in smooth layers, minimal turbulence, occurs at low velocities.

  • Turbulent Flow: Irregular fluctuations, larger pockets of air behind an object, occurs at higher velocities.

  • Types of Drag:

  1. Surface Drag - Friction between fluid and object surface.
  2. Form Drag - Resistance due to differently shaped pressure differential.
  3. Wave Drag - Resistance formed by waves at the fluid interface.

  • Bernoulli's Principle:

  • An increase in fluid velocity results in a simultaneous decrease in pressure.

  • Applications in sports include enhancing performance and minimizing drag during movement and flight.

  • Magnus Effect:

  • Describes the effect of rotation on the path of an object moving through a fluid.

  • Different types of spin (top spin, back spin, side spin) can influence trajectory and behavior in various sports.