The context of this question is looking at straggling in plasma. I was told there was a simple differential geometry relationship between the following entities: $$ \frac{dE}{dx},\; \frac{dE}{dy} \quad\text{and}\quad \frac{dE}{dt}, $$ where $x, y$ are distance in respective directions, $t$ is time and I'm using $E$ to denote mean kinetic energy of a particle.
So far the resources I've consulted don't show in a clear manner how to go about finding this relation, they remain in the abstract.
