An inclined plane is a straight surface that is slanted or tilted. It allows objects to move up or down with less effort than going straight up or down. It's like a ramp that makes it easier to move heavy things. Full definition
Science, for the most part, studies objects such as pendulums, steel balls on inclined planes, planets and stars. (religion-online.org)
So then, your contention is that when Galileo — that investigator so beloved and supposedly emulated by by deniers in other contexts — after having spent much time and effort showing that balls rolling down inclined planes followed a simple x * x equation he could not assume to have found a fundamental process at work? (realclimate.org)
Each Home Base's machine must include simple components such as inclined planes, wheels and axles, levers and pulleys. (edutopia.org)