slope is wi thangs roll down a hill, or a rode up the hill . . . steeper slope, faster it roll & bigger krash at the bottom . . . if 2 steep, yu kant go up, kauz yu keep sliding bak . . . in old daes, werkmen kall the slope=x%, . . . %=rise/run=how hi the vertikal part avter yu go horizontal bi "run" . . . it was eezee & praktikal for kommon werkmen tu du . . . even tudae, staers defined bi rise & run . . .