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I'm a physics graduate student.


2d
awarded  Nice Question
Mar
27
awarded  Good Answer
Mar
27
revised How small does sand have to be to get wet?
rolled back to a previous revision
Mar
26
awarded  Notable Question
Mar
26
awarded  Good Question
Mar
26
awarded  Nice Question
Mar
26
awarded  Popular Question
Mar
25
comment How does anything move?
Good point. I decided to change it to "can become positive" because I think the mere possibility is what was motivating the question.
Mar
25
asked How small does sand have to be to get wet?
Mar
25
revised How does anything move?
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Mar
25
awarded  Nice Answer
Mar
25
comment How does anything move?
...except those higher than six, of course, so the statement in my answer assumes the function is smooth. But worry about details like that is missing the point.
Mar
25
revised How does anything move?
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Mar
25
comment How does anything move?
The phrase "when the object starts moving" is a colloquial one, it doesn't have to mean the same thing as t=0. In your example, all the derivatives are positive at some time arbitrarily close to t=0.
Mar
25
answered How does anything move?
Mar
24
awarded  Popular Question
Mar
19
comment Noether Theorem and Energy conservation in classical mechanics
I find it hard to understand your question. The numerical value of the Lagrangian is not constant. It is not constant for infinitesimal periods. It is not constant for finite periods. The function form of the Lagrangian is usually constant. So if the Lagrangian is $\frac{1}{2}mv^2 - mgh$, it stays that, and doesn't become $\frac{1}{3}mv^2 - mgh$ at some later time or anything like that. The actual value of the Lagrangian of course changes because $v$ and $h$ change.
Mar
19
revised Do electromagnetic waves occupy varying amounts of space, or do they simply vary in magnitude?
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Mar
19
answered Do electromagnetic waves occupy varying amounts of space, or do they simply vary in magnitude?
Mar
18
revised If the gravity at the center of the Earth is zero, why are heavy elements like iron there?
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