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mascoteponto (November 30, 1999 at 12:00 am)
@QuaternionEMYou are absolutely correct. Every time I looked at it, I put it on the 7:30 mark, at which the expression was still incomplete. My apologies. =P
QuaternionEM (November 30, 1999 at 12:00 am)
@mascoteponto Yes, his second term does have the velocity squared.Here it is in black and white at 8:05.Just own your mistake and quit crying.
mascoteponto (November 30, 1999 at 12:00 am)
@QuaternionEMNo, his second term doesn't have velocity squared. :PBy the way, I'm not criticizing him, just pointing out what I think is a honest mistake on his part. I'd love have a tenth of his knowledge. :)
QuaternionEM (November 30, 1999 at 12:00 am)
From Dr Susskind's formula mj = (dF/dx)*a + (d²F/dx²)*v²1st term --> (N/m)*(m/s²) = N/s²2nd term --> (N/m²)*(m²/s²) = N/s²Your units from mj = (dF/dx)*a + (d²F/dxdt)*v1st term --> (N/m)*(m/s²) = N/s²2nd term --> (N/(m*s))*(m/s) = N/s²Yours works also but it still has a time derivative which we seek to eliminateto obtain an ODE rather than a PDE.
mascoteponto (November 30, 1999 at 12:00 am)
Sorry, I think you made a mistake. The term I meant to put there is not d²F/dxdt, but rather (d²F/dxdt)*v. You can easily see my answer is right by dimensional analysis: I'm sure we agree that his first term, (dF/dx)*a, is correct. Well, that is (force/distance)*(distance/time²) = force/time². His next term has different units, thus being wrong. It is (force/distance²)*(distance/time) = force/(distance*time). My correction, on the other hand, has the right dimensions. :)
QuaternionEM (November 30, 1999 at 12:00 am)
@mascoteponto I figured it out.It took me about 1/2 hour, but Dr Susskind is right again. The d²F/dxdt term can be written as d/dx(dF/dt) = d/dx(dF/dx*dx/dt) = d²F/dx² * v + dF/dx * d/dt(dx/dx)but dx/dx = 1 and d/dt(1) = 0So we get exactly what he said.QED
mascoteponto (November 30, 1999 at 12:00 am)
At about 7:30, doesn't he make a mistake? If he's deriving with respect to time, it should be:mj = (dF/dx)*a + (d²F/dxdt)*v
sephiroth317 (November 30, 1999 at 12:00 am)
@mexico0106 no f=mv is not a formula. you're thinking of p (momentum) = mv. don't have a clue why letters really matter -__- they're all variables anyhow
TheBubu983 (November 30, 1999 at 12:00 am)
I cant get past 5:37
SpazzzDog (November 30, 1999 at 12:00 am)
That's about as meaningful as saying Newtonian mechanics would be indeterministic if experiment confirmed it was indeterministic. |
