I've been able to derivate some function but not the following one: Code:

Dirac := (m dx[t])/(2 Sqrt[dx[t]^2 + dy[t]^2 + dz[t]^2])

.

I want to derivate the Dirac's function with respect to t. I tried Code:

D[Dirac[dx, dy, dz], t]

but then I get Code:

((m
\!\(\*SuperscriptBox["dx", "\[Prime]",
MultilineFunction->None]\)[t])/(
2 Sqrt[dx[t]^2 + dy[t]^2 + dz[t]^2]) - (m dx[t] (2 dx[t]
\!\(\*SuperscriptBox["dx", "\[Prime]",
MultilineFunction->None]\)[t] + 2 dy[t]
\!\(\*SuperscriptBox["dy", "\[Prime]",
MultilineFunction->None]\)[t] + 2 dz[t]
\!\(\*SuperscriptBox["dz", "\[Prime]",
MultilineFunction->None]\)[t]))/(
4 (dx[t]^2 + dy[t]^2 + dz[t]^2)^(3/2)))[dx, dy, dz]

which isn't what I'm looking for, I believe (I don't even know what this output mean). Notice that dx, dy and dz aren't the differentials x, y and z. Rather, they're functions which depends on t.

Any idea?