\[m = f(t).\]
\[1)\ Масса\ на\ \left\lbrack t_{1};\ t_{2} \right\rbrack:\]
\[m = \mathrm{\Delta}f = f\left( t_{2} \right) - f\left( t_{1} \right).\]
\[2)\ Средняя\ скорость\ на\ \left\lbrack t_{1};\ t_{2} \right\rbrack:\]
\[v_{ср} = \frac{\mathrm{\Delta}f}{\mathrm{\Delta}t} = \frac{f\left( t_{2} \right) - f\left( t_{1} \right)}{t_{2} - t_{1}}.\]
\[3)\ Мгновенная\ скорость:\]
\[v = f^{'}(t) = \lim_{\mathrm{\Delta}t \rightarrow 0}\frac{f(t + \mathrm{\Delta}t) - f(t)}{\mathrm{\Delta}t}.\]