I have written “Newton’s first law” so that those who have never learned physics can have a chance to learn about the wonderful ideas of the two great physicists, Galilei and Newton. To understand “Newton’s second law,” you have to understand what a vector is. The last article explains how one can relate the distance and the time an object falls due to gravity on Earth. It serves as a prerequisite for the articles listed in the section “Some basic ideas in General Relativity.”