I've gotten interested in the metallurgy of blades, and been watching a lot of early Forged in Fire. It's interesting to see basic applications with different blades by people who handle a lot of blades. There are fundamental similarities between blades of all types with the same primary functions, for instance, many of the knives and swords the smiths are challenged to create are used for hacking/chopping.
Length is the obvious answer, but here I'm asking about the physics of application—how are knife strikes mechanically different from sword strikes.
And length alone may not be the determining factor because a kris (dagger) can be up to 50 centimeters in length, which is within range of the Roman gladius and Ancient Greek xiphos (sword). The Spartan xiphos had even shorter blades of 30 cm (12 in), analogous to a long bowie knife.
Weight may be a factor, but not all the sources I'm using list blade weights, and this factor seems also omitted from FOF.