This document provides an overview of basic physics concepts. It begins by defining SI base units such as meters, kilograms, and seconds. It then discusses derived SI units for area, volume, density, velocity, and other concepts. The document outlines the structure of atoms including protons, neutrons, and electrons. It also defines atomic number, mass number, and isotopes. Additional sections cover states of matter, changes between states, and mechanical properties of matter. In the mechanics section, the document defines concepts such as stress, strain, pressure, and buoyancy in fluids.