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For example if the force on a particle is of the form $ \mathbf F = \mathbf F(\mathbf r, \dot{\mathbf r}, \ddot{\mathbf r}, \dddot{\mathbf r}) $, then the equation of motion would be a third order differential equation, what will require us to know the initial conditions $ \mathbf r(0), \dot{\mathbf r}(0), \ddot{\mathbf r}(0) $ in order to get the exact solution.

EDIT: As akhmeteliless mentioned the Abraham–Lorentz force is an example for such force. But, how such force is possible if the Lagrangian contains only the coordinates and their first time derivatives? Shoudn't the equations of motion be second order differential equations?

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Related: physics.stackexchange.com/q/4102/2451 and links therein. – Qmechanic Jan 24 at 8:39
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Just a tip: if you feel that the question could be answered more fully, it's best not to accept an answer, because that tends to discourage people from posting another one. Personally, I would very much like to see a more comprehensive answer to this question. – Nathaniel Feb 12 at 1:41

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For example, the Dirac-Lorentz equation.

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How such force is possible if the Lagrangian contains only the coordinates and their first time derivatives? Shoudn't the equations of motion be second order differential equations? – Andrey B Jan 24 at 3:24
For what it's worth, it is written in a book by I. M. Ternov e.a. "Synchrotron Radiation and its Applications" (books.google.com/… ) that the Dirac-Lorentz equation "cannot be derived from a Hamiltonian or a Lagrangian, because it takes into account the radiation frictional force and thus describes a nonconservative system." I am not sure, but... – akhmeteli Jan 24 at 5:26
OK than, thanks. – Andrey B Jan 24 at 9:52

The Equation of Motion can be 2nd order only in some particular cases. The general equation of motion shall have to be the 3rd order differential equation.Newtons 2nd Law in form of 2nd order differential equation failed to describe the motion of micro particles not because the micro particles behave as fictitious waves but because it is 2nd order. In fact the Operator Formalism of Quantum Mechanics is indirectly based on this fact and the Quantum Motion Laws can be derived from Newtons 2nd Law of 3rd order. I can give an elaborate picture of this if desired.

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