Quite apart from effects due to Earth's rotational and orbital motions, a laboratory reference frame is not strictly an inertial frame because a particle at rest there will not, in general, remain at rest; it will fall. Often, however, events happen so quickly that we can ignore the gravitational acceleration and treat the frame as inertial. Consider, for example, an electron of speed v = 0.992c, projected horizontally into a laboratory test chamber and moving through a distance of 20 cm.
(a) How long would that take, and
(b) How far would the electron fall during this interval?
(c) What can you conclude about the suitability of the laboratory as an inertial frame in this case?