In E-M problems, it may be needed to find the position of any particle at some time t', given the fields acting on it. From the E-M field theory, we will be able to obtain the force acting on the particle. After that we can find the position from this class' methods.
Though I don't think this pollutes the API since these are kwargs. We can improve it over the summer to read better, but I feel a general purpose vector calculus package should have all kinds of functionality, not necessarily EM or mechanics specific.