Consequently, also length contraction can not be measured by co-moving observers.
en.wikipedia.org Special relativity implies a wide range of consequences, which have been experimentally verified, including length contraction, time dilation, relativistic mass, massenergy equivalence, a universal speed limit, and relativity of simultaneity.
en.wikipedia.org Because of its high velocity, the ladder undergoes the relativistic effect of length contraction, and becomes significantly shorter.
en.wikipedia.org But this is not strictly correct, since length contraction and time dilation having their exact relativistic values are sufficient but not necessary for the explanation of both experiments.
en.wikipedia.org If the direction of motion is perpendicular to the "plates", length contraction of the plates does not occur, but the distance between them is reduced.
en.wikipedia.org