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2:25 AM
Q: Why do we not observe a greater Casimir force than we do?

John DumancicI am very new to quantum field theory, so forgive me if this question is a bit silly. The Casimir force is usually explained by the zero point energy of the field. You assume that the frequencies of the field are quantized between the two plates, perform some regularization, and out pops, for the...

3 hours later…
5:46 AM
Q: Varying the action with respect to the metric in one dimension

VirgoI am reading Witten's interesting article What every physicist should know about string theory. On page 39 he gives the general relativistic action in one spacetime dimension of a scalar fields $X_I$, with $I=1\ldots D$: $$ I=\int d t \sqrt{g}\left[\frac{1}{2} \sum_{I=1}^{D} g^{t t}\left(\frac{d ...

5 hours later…
10:23 AM
Q: Why do we neglect torque caused by tension of curved part of rope in massive pulleys?

BuraianIn this MIT OCW lecture, the professor analyzes a block - massive pulley - block system as shown here: The analysis was easy enough to follow till this point: Here he says the only the end points of the curved segment causes the pulley to be torqued.. why is this?

Q: Can concepts like "critical damping" or "resonant frequency" be applied to more complex systems than just a spring and damper in parallel?

mikeI am trying to do some modeling analysis by representing materials with parallel systems of springs and dampers. In the simplest case with just one spring parallel to a damper, we have the traditional "damped oscillator": The fundamental resonant angular frequency is given by: $$ω = \sqrt{\frac{...

10:55 AM
Q: Deleting my account in PSE

A plus bNo offense meant i am writing here but it's of physics stack exchange ,my whole account has been deleted there and no reason(removed by moderator) has been given in PSE . I had asked my 5th question . Every thing is deleted . How to recover it? The questions has meaning for me and each of my ques...

7 hours later…
5:59 PM
Q: Fundamental "definition" of momentum

satan 29In introductory classical mechanics, we come across the quantity momentum defined as $p=mv$. There seems to be no other "definition" of momentum, (apart from the vague "measure of quantity of motion") and the only role it seems to play is in defining the force $F$ in Newton's second law $F=\dfrac...

3 hours later…
8:59 PM
Q: Why do wet plates stick together with a relatively high force?

Jan StullerWhen I wash up plates and don't dry them right away and place on top of each other, they seem to stick together with a relatively high "force": i.e. when I try to pick the top plate hours later, the bottom plate sticks to the plate that I try to pick up to the point that it "beats" gravity. What...


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