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Thomas2054
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In reading Feynman's "Lectures on Physics", volume 2 I have a question and have included a scan of a small section from the book.
Feynman was a big fan of using the Principle of Virtual Work, but his explanation, as least insofar as how he used it is wanting, at least for me.
The attached pdf refers to the torque on a current carrying loop. It is largely how he uses algebraic signs that throw me. In this example you can see where he is applying the principle and says, "The principle of virtual work says that the torque is the rate of change of energy with angle, …" and then he throws in the negative sign on the expression of that thought. Then, just below he sets tau to the negative of how he previously defined it just a few lines above. I agree with the final outcome, equation (15.3), but I would not have used the negative signs in either the expression for dU or for tau.
Can someone enlighten me as to his thinking?
Thanks.
Thomas
Feynman was a big fan of using the Principle of Virtual Work, but his explanation, as least insofar as how he used it is wanting, at least for me.
The attached pdf refers to the torque on a current carrying loop. It is largely how he uses algebraic signs that throw me. In this example you can see where he is applying the principle and says, "The principle of virtual work says that the torque is the rate of change of energy with angle, …" and then he throws in the negative sign on the expression of that thought. Then, just below he sets tau to the negative of how he previously defined it just a few lines above. I agree with the final outcome, equation (15.3), but I would not have used the negative signs in either the expression for dU or for tau.
Can someone enlighten me as to his thinking?
Thanks.
Thomas