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Newton’s Laws of Motion

1) Newton’s first law

An object continues in a state of rest or uniform motion in  a straight line unless acted on by a resultant force.

2) Newton’s second law

The rate of change of momentum of an object is directly proportional to the resultant force applied and is in the direction of the resultant force.


  • F = resultant force in newtons (N)
  • m = mass in kilograms (kg)
  • a = acceleration in metres per second per second (ms-2)

rate of change of momentum 2

  • F  = resultant force in newtons (N)
  • D(mv) = change in momentum in kilogram metres per second (kg ms-1)
  • t = change in time in seconds (s)

3) Newton’s third law

When two objects interact they exert equal and opposite forces on each other.