Lecture on Newton's Laws and Biomechanics

Overview

• Review of Newton's laws of motion in the context of biomechanics and human movement.

Newton's First Law

• Inertia:
  • Objects resist changes in motion.
  • Related to mass: greater mass = greater inertia.
  • Requires an external force to change state of motion.

Newton's Second Law

• Law of Acceleration:

  • Change in motion proportional to force impressed.
  • Formula: Force = Mass x Acceleration.
  • Acceleration depends on force magnitude and object mass.
  • Example: Baseball vs. shot put - less mass accelerates more.

• Impulse:

  • Product of force and time duration.
  • Important for momentum changes in physical activities.
  • Graphical Representation: Force on y-axis, time on x-axis. Area under curve = impulse.
  • Longer force application = greater impact; shorter time = greater force needed.

• Momentum:

  • Momentum = Mass x Velocity.
  • Impulse changes momentum (generally changes velocity).
  • Example: Football lineman vs. toddler – mass and velocity affect momentum.
  • Conservation of momentum in collisions - consistent unless external forces act.

Types of Collisions

• Elastic Collisions:

  • Momentum completely transferred, objects bounce off.
  • Perfectly Elastic: Equal masses, velocities reversed post-collision.
  • Coefficient of Restitution: Measures elasticity; 1.0 for perfectly elastic, 0.0 for inelastic.

• Inelastic Collisions:

  • Objects stick and move together post-impact.
  • Momentum conserved, velocity shared.

Practical Applications

• Impulse-Momentum in Sports:

  • Catching ball: Soft techniques increase time, reduce peak force impact.
  • Vertical jumps: Optimize force and time for effective jump height.

• Landing Mechanics:

  • Soft landings reduce mechanical load via increased contact time, lowering injury risk.

Newton's Third Law

• Action-Reaction Principle:

  • Forces occur in pairs, equal in magnitude, opposite in direction.

• Movement Applications:

  • Reaction forces essential in walking, jumping, throwing.

Friction

• Role in Movement:

  • Acts parallel to contacting surfaces; crucial for stability and performance.
  • Coefficient of Friction: Determines force needed to overcome friction between surfaces.

• Example of Friction:

  • Pulling a sled with considerations for frictional forces and angles.
  • Static vs. Kinetic Friction - differences in overcoming initial movement vs. maintaining motion.