Average velocity

Gist: Displacement over an interval divided by that interval. Signed — the sign says which way the object ended up relative to where it started.

${\bar{V}}_{t_1{t}_2}=\frac{x_{t_2}-x_{t_1}}{t_2-t_1}$

Why it matters: Three cases fix the idea: $>0$ moving along $+x$, $=0$ back at the same position, $<0$ moving against $+x$. Only the endpoints enter the formula, so it says nothing about the path taken between them.

Detail: Lecture 2, p.1

Related: Average speed, Instantaneous velocity, Sign convention, Physics