Background Let x= x and v. be the position and velocity of a particle att = t , while x = x, and vy be the position and velocity of a particle at t = to, with t, > t . The one-dimensional displacement vector is a signed number given by Ax= x -XI. (4.1) The time elapsed as the particle moves from x to x is just A=t-t. (4.2) The average velocity betweent, and to is Ax (4.3) At If t, and t are very very close, so that At = t, -t is very very small then the velocity is the so-called instantaneous velocity. Ax = (At - 0). (4.4)