The beginnings of modern science are traced back to relatively obscure figures, such as Pierre Gassendi, credited with the first concept of gravity, and early «atomicists», such as the «Mad Duchess», Margaret Cavendish, who believed in four types of atoms — square, long, round and sharp. (newscientist.com)
It refers to both the physical concept of gravity — as in the force that presses matter towards the Earth — as well as the notion of something being grave and serious. (mocaga.org)
She is learning the concept of gravity when you pick up her toys or other objects through her dropping. (shrewdmommy.com)