Average acceleration

Gist: Change in velocity divided by the time it took.

$\bar{a}=\frac{\Delta v}{\Delta t}$

Why it matters: A small $\Delta t$ makes $\bar{a}$ enormous, which is why impacts break things. A tennis ball reversing from $-5$ to $+5$ m/s in about $10^{-2}$ s averages

$\bar{a}=\frac{5-(-5)}{10^{-2}}=10^3{\text{m/s}}^2$

Detail: Lecture 2, p.4

Related: Instantaneous acceleration, Average velocity, Physics