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Trouble with definition of Newton's First Law

  1. Apr 20, 2015 #1
    The lecturer in my dynamics class defined Newton's First Law to be 'There exists at least one inertial frame with respect to which mass m moves in a straight line with a constant velocity. In this frame no net force acts on m.'

    This has confused me; I thought inertial frames could not accelerate? Therefore how can this be true if mass m is accelerating? How can the frame 'keep up'?
  2. jcsd
  3. Apr 20, 2015 #2


    Staff: Mentor

    What was the full context of the discussion. Was he referring to objects falling/acelerating on the Earth?

    If you fall with the object then to someone on the Earth you and object would be accelerating. However, relative to you, you and the object are in an inertial frame of reference.

  4. Apr 20, 2015 #3
    Ah I see, thanks for clearing that up :)
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