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Section C.1 Writing

Subsection C.1.1 introduction

Omit needless words. Vigorous writing is concise.

A sentence should contain no unnecessary words, a paragraph no unnecessary sentences, for the same reason that a drawing should have no unnecessary lines and a machine no unnecessary parts. This requires not that the writer make all his sentences short, or that he avoid all detail and treat his subjects only in outline, but that every word tell.

―Strunk and White, The Elements of Style

Bad —“The type of friction which Statics focuses on is dry friction.”

Good —“Statics focuses on dry friction.”

Bad —“All normal forces on a FBD should be pointing at (and not away from) the body.”

Good —“Normal forces on a FBD should point towards the body.”

Consistency.

What's our point of view? It is all over the place in the text.

Formal or informal?

Are we directing and guiding the students? “You start by...”

Are we collaborating with the students? “We can see that...”

Are we the wise sage. “Let us transition to the forces...”

Should we avoid pronouns and just make statements. “The result is...”

  • Say free-body diagram, not free body diagram, alternately you can say FBD. Never say FBD’s; you mean FBDs.
  • Say two-dimensional problem, not 2D problem or “two dimensional”
  • Say zero-force member
  • There is no hyphen in two dimensions.
  • \(x\) axis, not \(x\)-axis.
  • use double quotes <q> to set off a word as a word, or better still if it is a term, use <term> tag.
  • Use unordered lists when order is not significant. Use ordered lists for things that need to be numbered, like a procedure.
  • Punctuate ordered lists with periods at the end of each item. Punctuate unordered list like one long sentence i.e., commas or semicolons at the end of each item except the last, which gets a period
  • No “use your equations of equilibrium” Yes“the equations of equilibrium.”
  • Spell out clockwise and counter-clockwise, unless in space is limited, like in a table or caption.
  • Spell out numbers less than ten.
  • Maintain consistent capitalization in chapter/section titles - use title case.
  • Keep titles short enough to fit in one line in the pretext sidebar.
  • Keep an eye out for 'emphasis' quotes or ALL CAPS. Instead use the <em> tag.
  • Statics or statics or mechanics? I say statics for the subject, and Statics for the course.

Subsection C.1.2 Units

Pretext doesn't have great support for units, but they are very important for engineering, so I have cobbled together a workaround.

Whenever you have a quantity with units, you need to include it in the source code using one of the macros below, and put this in a math environment like <m>, <me>, or <md>.

The values inside the brackets can be a bare number, or any valid math.

By doing this, when the book is turned into html or pdf, the units will be rendered correctly, Upright font in a math environment, superscripts etc.

See samples below.

If you need a unit which is not here, add it a new macro to the doc info

  1. \kg{100} produces \(\kg{100}\)

  2. \lbm{100} produces \(\lbm{100}\)

  3. \slug{100} produces \(\slug{100}\)

  4. \m{100} produces \(\m{100}\)

  5. \cm{100} produces \(\cm{100}\)

  6. \mm{100} produces \(\mm{100}\)

  7. \km{100} produces \(\km{100}\)

  8. \ft{100} produces \(\ft{100}\)

  9. \inch{100} produces \(\inch{100}\)

  10. \N{100} produces \(\N{100}\)

  11. \kN{100} produces \(\kN{100}\)

  12. \MN{100} produces \(\MN{100}\)

  13. \lb{100} produces \(\lb{100}\)

  14. \lbf{100} produces \(\lbf{100}\)

  15. \Nm{100} produces \(\Nm{100}\)

  16. \kNm{100} produces \(\kNm{100}\)

  17. \ftlb{100} produces \(\ftlb{100}\)

  18. \inlb{100} produces \(\inlb{100}\)

  19. \lbperft{100} produces \(\lbperft{100}\)

  20. \Nperm{100} produces \(\Nperm{100}\)

  21. \kgperkm{100} produces \(\kgperkm{100}\)

  22. \aSI{9.8} produces \(\aSI{9.8}\)

  23. \aUS{32.2} produces \(\aUS{32.2}\)

  24. \unit{1} produces \(\unit{1}\)

  25. \ang{30} produces \(\ang{30}\)

Some Examples.

Here are a few examples of the units macros used in other situations

\begin{align*} P \amp = \unit{0.438} \times (\lb{100} / \unit{}) \\ \amp = \lb{43.8} \text{ at } 10° \measuredangle\\ N \amp= \unit{1.02} \times ({\lb{100}}/ \unit{}) \\ \amp = \lb{102} \text{ at } 115° \measuredangle \end{align*}

This is kind of a hack, but there's no space after the distance units, so you can raise them to powers after the macro. This means we don't have to create macros for m^2, ft^3 etc. If these macros need to get replaced with something better, watch out for these when grepping.

  1. \ft{100}^2 produces \(\ft{100}^2\)

  2. \inch{100}^3 produces \(\inch{100}^3\)

  1. \(\displaystyle A = \ft{\frac{b \times h}{2}}^2\)
  2. \(\displaystyle I_{xx} = \mm{2.4 \times 10^6}^4\)
\begin{align*} \left|\vec{AB}\right |\amp =\sqrt{(\Delta_x)^2+(\Delta_y)^2+(\Delta_z)^2}\\ \amp =\sqrt{(\m{-4.5})^2+(\m{-1.5})^2 + (\m{4.3})^2 }\\ \amp =\sqrt{\m{40.99}^2 }\\ \amp \simeq \m{6.402}\\ \\ \mathbf{F}_{AB} \amp = F_{AB} \; \widehat{\mathbf{AB}}\\ \amp = \kN{5} \left \langle -0.7,-0.23,0.67\right \rangle\\ \amp = \kN{ \left \langle -3.51,-1.17,3.36 \right \rangle } \end{align*}