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Re: Landau & Lifschitz, Mechanics, Principle of Least Action
Posted:
Jan 17, 2014 2:28 AM


On Wed, 15 Jan 2014, Hetware wrote:
> On page 3 of Landau & Lifschitz's Mechanics it is stated that > > delta qdot = d(delta q)/dt.
> This fact is not demonstrated, it is asserted. qdot is a vector /tangent to/ > the particle trajectory. deltaq is a displacement /of/ that trajectory. I > see no a priori reason to believe the two are interchangeable.
pho = position vector = q tau = tangent vector = qdot tau = dpho/dt
delta tau(t) = tau(t + delta t)  tau(t) = dpho(t + delta t)/dt  dpho(t)/dt = d(pho(t + delta t)  pho(t))/dt = d(delta pho(t))/dt



