Four-force
= Four-force
{title2=$K^\mu=dp^\mu/d\tau$}
{wiki}
The <four-force> is the <proper time> derivative of <four-momentum>. For constant rest mass and coordinate three-force $\mathbf F=d\mathbf p/dt$, its components are $K^\mu=\gamma(\mathbf F\cdot\mathbf v/c,\mathbf F)$ in the convention $p^\mu=(E/c,\mathbf p)$. Thus it packages the power transfer and three-force into one Lorentz-covariant vector.