This article presents concepts of Riemannian geometry and apply them to a two-dimensional sphere, the sphere S2, which is the simplest Riemannian manifold. Thus this article is intended to give enough subsidies to undergraduate students of physics to understand such concepts of geometry in order to facilitate the study of the general relativity. Similarly, this article is suitable to high school teachers who want to use basics concepts of Riemannian geometry to talk about the progress made in the field. In this sense, we introduce the curvature and define the manifold S2, showing that its curvature is not zero. This illustrates the theoretical framework of general relativity and it shows how the familiar concepts in Euclidian geometry change when the geometry is expanded. As an example we show how the Pythagorean theorem is built on this manifold.
Riemannian geometry; general relativity; metric tensor
