Biomechanics: Newton's Laws of Motion

Newton's First Law of Motion: Inertia

  • A body remains at rest or in uniform motion unless acted upon by another force.

  • Inertia is directly proportional to mass.

  • Greater mass requires greater force to change motion.

  • To overcome inertia, apply force proportional to the body's mass.

Newton's Second Law of Motion: Acceleration

  • F=maF = ma (Force = mass x acceleration).

  • Acceleration is proportional to force and inversely proportional to mass.

  • Momentum (p) = Mass (m) x Velocity (v).

  • Impulse = Ft (Force x time).

  • Increase time to absorb force and decrease risk of injury.

Newton's Third Law of Motion: Action-Reaction

  • For every action, there is an equal and opposite reaction.

  • Forces work in pairs.

  • Ground force reaction: runner pushes back, ground pushes forward.

  • Large mass minimizes the effect of action force (e.g., Earth not pushed back by a runner).