When the magnetic fields are capable of modifying an individual particle trajectory, it is said that the plasma is magnetized.
The curvature of the particle trajectories is proportional to mass density.
Newton's law of motion, however, had to be modified to provide consistent particle trajectories.
In the magnetotail, however, particle trajectories seem to constantly reshuffle, probably when the particles cross the very weak field near the equator.
It is used to measure the particle trajectories close to the interaction point in order to precisely separate primary and secondary vertices.
The principle of this method is based on the fact that particle trajectories in gravitational fields are geodesics.
Thus, to define particle trajectories, one needs an additional rule that defines which space-time points should be considered instantaneous.
Even a whole particle trajectory can be measured by a weak measurement.
When waves propagate in shallow water, (where the depth is less than half the wavelength) the particle trajectories are compressed into ellipses.
The rays of geometrical optics are not unlike the particle trajectories of classical mechanics.