Biomechanics 2

Newton’s 3 Laws of Motion

  1. Law of Inertia/Momentum

  2. Law of Acceleration

  3. Law of Action/Reaction

Newton’s Law of Inertia (1st Law)

— an object at rest will remain at rest unless acted upon by a force, just as an object in movement will stay in movement unless acted upon by another force

Newton’s Law of Acceleration (2nd Law)

— the acceleration of an objet depends on the mass of the object and the force applied

  • force = mass x acceleration

  • momentum is the rate of change of velocity

  • measured in m/s² = N

Newton’s Law of Action/Reaction (3rd Law)

— for every action there is an equal opposite reaction

  • for all objects moving and static

Linear Application

Equilibrium

— net force equals zero

  • all forces acting on an object sum to zero

— can be both static and dynamic

  • static: system is at rest and all forces equal 0

  • dynamic: object in motion with net forces equal 0

Ground Reaction Forces (GRF)

— force made by the ground in reaction to a force made by a body on the ground

  • ground reaction forces in walking and running:

  • reflects the acceleration of the total body center of mass

Friction

— force that resets relative tangential (linear) motion

  • factors that affect friction:

  • types of material

  • force holding objects together

  • substances between surfaces

Momentum

— the quantity of motion if an object in motion

  • momentum = mass x velocity

  • units are kg x m/s

Power

— amount of work (energy transferred to/from object) done over a period of time

  • power = (force x displacement) / time

Angular Applications

— all parts of a body/object move along a circular path about an axis

  • exactly in the same angle

  • in same direction

  • in the same time