According to general relativity, the spacetime is a four-dimensional object that has to obey an equation, called the Einstein equation, which explains how the matter curves the spacetime.

I teach two-semester College Physics and General Physics curricula often. The first course covers kinematics, dynamics, energy, momentum, rotational and harmonic motion, waves, fluid dynamics, heat, ...

I had planned for part 2 of this series about π to be about the classical area formula for the circle, but then something new came up. Well, by new I mean a new proof of something old, and it's a ...