title_body: What software is used by the publishing companies to create diagrams in the introductory physics textbooks?
upvoted_answer: They are almost certainly done in TeX/LaTeX. TeX/LaTeX is not about "less effort", but exactness. It is a programming language for typesetting with a special emphasis on math and equations. TeX has a long history with the academic community in publishing. Explaining TeX and LaTeX is outside the scope of this forum (There is a TeX.stackexchange.com site). You can find some examples of how those types of diagrams are done here:
  
  http://www.texample.net/tikz/examples/tag/diagrams/