Curved Spacetime (Gravity) Tells Mass (Energy) How to Move

Consider the fall of the apple that, by legend, hit Newton on the head. Instead of using this to introduce Newton's law of gravity, we will discuss the point of view that the fall of the apple was caused by a minuscule curvature of spacetime in the region surrounding Newton and the apple tree. We will calculate this curvature using concepts and equations entirely appropriate for students in an introductory physics course. The result introduces the idea that if gravity curves spacetime, perhaps curved spacetime can ripple in such a way as to create a gravitational wave that tells us what happened to two black holes 1.3 billion years ago. © 2018 American Association of Physics Teachers.