Newton's Second Law
Forces and Motion

When the resultant force is not zero

Physics Narrative for 11-14 Supporting Physics Teaching

Resultant forces change motion

  • Most moving objects are acted upon by a driving force and retarding (often frictional) forces acting in the opposite direction to the motion.
  • When these forces add to zero (the resultant force is zero), the object maintains a constant speed.
  • When the forces do not add to zero (there is a non-zero resultant force), the object will either speed up, slow down or change direction.
Newton's Second Law
is expressed by the relation F=ma
can be used to derive Kepler's First Law

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