Trouble with definition of Newton's First Law

AI Thread Summary
Newton's First Law defines an inertial frame as one where a mass moves in a straight line at constant velocity with no net force acting on it. This can be confusing when considering accelerating objects, as it seems to contradict the definition of inertial frames. However, if an observer falls with an accelerating object, they are in a non-inertial frame, while the object appears to move at constant velocity relative to them. The discussion clarifies that inertial frames can exist even when objects are accelerating relative to other frames, such as when falling on Earth. Understanding this distinction helps reconcile the concepts of motion and reference frames.
Rwindsor1
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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'?
 
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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.

http://en.wikipedia.org/wiki/Inertial_frame_of_reference
 
Ah I see, thanks for clearing that up :)
 

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