Susan, an apple falling from a tree is an instance of the workings of gravity. Same with leaves falling in the Fall. Same as Galileo dropping things from the leaning tower of Pisa. Science explains things we experience in the world out there.
Gravity is a force that we see working but we do not see in itself. It is not supernatural but gravity is also not imaginary. There is still some debate in physics over the exact nature of gravity but the recent discovery of gravity waves is helping seal the deal. That said, things as simple as apples falling from trees are instances of gravity. Things in the world are ultimately what we are talking about!