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Why can friction make observing Newton's first law of motion difficult?
Where did you find this definition? What is meant by "uniformly?"Originally posted by Stingray
Newton's first law is kind of circular. We define the net absence of forces to be the state where an object moves uniformly.
i think he meant constantly or at rest.Originally posted by turin
Where did you find this definition? What is meant by "uniformly?"
Based on this, I can see why you think it is a circular definition. I myself had this problem not very long ago (I thought that the definition of "inertial frame" was circular, but I think it might be the same fundamental issue). The good news, at least for me, is that I got the conflict resolved, with the help of sereral contributors (of whom lethe was not the least).Originally posted by Stingray
Yes, that's what I meant. Uniformly meant "without acceleration."
Force is most naturally defined though newton's 2nd law (generalization of the 1st law). What other definition would you like?
We seem to be thinking of different things. I didn't have an issue with the definition of an inertial frame. My internal picture was similar to what you described.Originally posted by turin
Now, Newton's first law says that free particles will move in straight lines with respect to such a frame (assuming space is flat).
This is not true. A free particle is one that moves through a region of constant potential without constraint (since this is Newton's law, we're talking about mechanics in 17th century terms). This itself says nothing of the shape of the trajectory. That's where Newton's first law comes in. Given that there is no potential gradient and no surface onto which the particle is constrained, Newton says that the trajectory of such a particle is straight in an inertial frame and the velocity does not change.Originally posted by Stingray
In your statement that I am quoting, I meant that labeling the particle as "free" is defined by its straight-line motion.
I'll have to think about this one. Just off the top of my head, I would say that you can, because energy is an abstraction that does not require a trajectory, so the same can be said of a potential, which is closely related to energy (energy/interaction factor). IMO, Newton's first law is how a potential affects a trajectory, and that the definition is just backwards, not circular.Originally posted by Stingray
You can't define potentials without talking about how they affect trajectories.
Yes, I agree. I think that would be a good reason why friction makes the first law difficult to observe.Originally posted by Stingray
Also, the title of this thread is a force that can't be described by a potential![]()
I don't see how this is circular. What if we defined the net absence of forces to be when a body accelerates at 1 m/s2. Would that be circular? In any event, if Newton's first law were a definition, then we could writeOriginally posted by Stingray
Newton's first law is kind of circular. We define the net absence of forces to be the state where an object moves uniformly.
Newton's first law is not a definition, is it?Originally posted by StephenPrivitera
if Newton's first law were a definition, then we could write
No net forces act upon a body if and only if the body moves uniformly.
No it is not, that was part of my point.Originally posted by turin
Newton's first law is not a definition, is it?