Page 14, he unpacks the distinction between speed and velocity with an example of spheres moving in different directions on a smooth table, and describes them moving in perpendicular paths at the same speed, asserting that their velocities are different although their respective speeds each read the same number. At this point in his account, he seems to have begged the question of direction itself, and of the idea of identity.
Say that the same two spheres are each moving at the same uniform speeds along a smooth table, but are in parallel paths, or at least as far as is practical to measure, parallel paths.
Can they be said, according to his distinctions so far, to have the same velocity or velocities or not?
Does it make any sense to say that the velocity of spheres moving in parallel paths at the same speed and over the same time interval is identical?
Or would his account of these be the same as that of the perpendicular spheres, that their velocities also are different? They are, after all, in different positions. Say two parallel cars, adjacent lanes, along a one way street.
Einstein has said he prefers to begin with the simplest examples.
Isn't the idea of direction itself bound up also with those of identity, position, uniqueness, etc?
Thus, doesn't the law of inertia itself imply or entail, if not express, them somehow?
Or is it merely premature, and impertinent, to challenge the rectitude of his order of exposition of these ideas?
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