Abstract:
The ways for improving on techniques for finding new solvable potentials based on supersymmetry and shape invariance has been discussed by Morales et al. [1] In doing so they address the peculiar system known as the one-dimensional hydrogen atom. In this paper we show that their remarks on such problem are mistaken. We do this by explicitly constructing both the one-dimensional Coulomb potential and the superpotential associated with the problem, objects whose existence are denied in the mentioned paper.

Abstract:
The effect of quenched disorder on the underdamped motion of a periodically driven particle on a ratchet potential is studied. As a consequence of disorder, current reversal and chaotic diffusion may take place on regular trajectories. On the other hand, on some chaotic trajectories disorder induces regular motion. A localization effect similar to {\sl Golosov Phenomenon} sets in whenever a disorder threshold that depends on the mass of the particle is reached. Possible applications of the localization phenomenon are discussed.

Abstract:
We analyse the motion of a sphere that rolls without slipping on a conical surface having its axis in the direction of the constant gravitational field of the Earth. This nonholonomic system admits a solution in terms of quadratures. We exhibit that the only circular of the system orbit is stable and furthermore show that all its solutions can be found using an analogy with central force problems. We also discuss the case of motion with no gravitational field, that is, of motion on a freely falling cone.

Abstract:
The curve joining the points of maximum height in the parabolas of ideal projectile motion is shown to be an ellipse. Some features of the motion are illustrated with the help of such ellipse.

Abstract:
the magnitude of an electric dipole moment must be larger or equal to a certain critical value to support bound states. this is not a widely known fact that nevertheless is easy to understand on heuristic terms and relatively easy to calculate. this critical dipole moment, , has been calculated in 2 and 3 dimensions. it has been ascertained that it does not exist in one dimension or, at least, that it is not computable. in this work, after giving simple arguments on the existence of this critical moment, we compute in one dimension.

Abstract:
The magnitude of an electric dipole moment must be larger or equal to a certain critical value to support bound states. This is not a widely known fact that nevertheless is easy to understand on heuristic terms and relatively easy to calculate. This critical dipole moment, , has been calculated in 2 and 3 dimensions. It has been ascertained that it does not exist in one dimension or, at least, that it is not computable. In this work, after giving simple arguments on the existence of this critical moment, we compute in one dimension. El valor de un momento dipolar eléctrico debe ser mayor o igual a un valor crítico para que admita estados ligados. Este no muy conocido hecho puede comprenderse en forma muy simple y su valor calculado en forma relativamente simple como lo hacemos en este trabajo. Se ha calculado el momento crítico en 2 y 3 dimensiones y se ha sugerido que no existe en una dimensión o que, al menos, no se le puede calcular. Damos argumentos simples para argüir su existencia y lo calculamos exactamente en una dimensión.

Abstract:
The effects of quenched disorder on the overdamped motion of a driven particle on a periodic, asymmetric potential is studied. While for the unperturbed potential the transport is due to a regular drift, the quenched disorder induces a significant additional chaotic ``diffusive'' motion. The spatio-temporal evolution of the statistical ensemble is well described by a Gaussian distribution, implying a chaotic transport in the presence of quenched disorder.

Abstract:
A variational principle is proposed for obtaining the Jacobi equations in systems admitting a Lagrangian description. The variational principle gives simultaneously the Lagrange equations of motion and the Jacobi variational equations for the system. The approach can be of help in finding constants of motion in the Jacobi equations as well as in analysing the stability of the systems and can be related to the vertical extension of the Lagrangian formalism. To exemplify two of such aspects, we uncover a constant of motion in the Jacobi equations of autonomous systems and we recover the well-known sufficient conditions of stability of two dimensional orbits in classical mechanics.

Abstract:
We discuss a recently proposed variational principle for deriving the variational equations associated to any Lagrangian system. The principle gives simultaneously the Lagrange and the variational equations of the system. We define a new Lagrangian in an extended configuration space ---which we call D'Alambert's--- comprising both the original coordinates and the compatible ``virtual displacements'' joining two solutions of the original system. The variational principle is Hamilton's with the new Lagrangian. We use this formulation to obtain constants of motion in the Jacobi equations of any Lagrangian system with symmetries. These constants are related to constants in the original system and so with symmetries of the original Lagrangian. We cast our approach in an intrinsic coordinate free formulation. Our results can be of interest for reducing the dimensions of the equations that characterize perturbations in a Lagrangian control system.