clod of earth, lump of soil
坷 centers on a small, solid piece of earth: a clod or lump of soil. The two given meanings are essentially the same concrete image.
坷 combines 土 (earth) with 可, which likely contributes the sound. The character expresses a lump of earth.
The left side is earth 土, and the right side 可 looks like a mouth 口 with a hook above. Imagine a mouth spitting out a clod of soil: 坷 is a lump of earth.
For カ, picture a car (カ) driving over a clod of earth and bumping: car -> カ, and the lump of soil makes the ride rough.
—