# TAM 251: Introductory Solid Mechanics

PrairieLearn and CBTF tips:

• Error tolerance is $1\%$. This (roughly) corresponds to using three 3 significant figures
• NOTE: By default, Matlab displays five digits of any stored variable -- NOT five significant digits (this is "format short"). If that variable is a small number (as strain values commonly are), this can lead to fewer than three significant digits being displayed.

For example, you may (correctly) compute a strain value of x = 1.17*10^(-3) using symbolic expressions. If you ask Matlab to print x, it will return x = 0.0012 (exactly five digits, and two significant digits). However, PrairieLearn will mark the answer 0.0012 incorrect, as the difference between these two values is about 2.5% (that is, (1.2-1.17)/1.17 = 0.0256) and exceeds PL's tolerance for correct answers.

Note that Matlab has not rounded the actual stored value; only the displayed value. You can ask Matlab to always print the full stored value by entering the command "format long" before computing. Matlab will then print 0.00117, to full precision. Be careful, as this setting reverts to "format short" when you close Matlab!

• Do not use fractions as your input answer. Instead use decimal numbers (e.g. 2/3 is not accepted as a correct answer, however 0.667 is)
• The CBTF desktop calculator and Mathematica use radians instead of degrees for angle calculation. If you want to evaluate the cosine of a $30^o$ angle, you should evaluate $\cos[30 \frac{\pi}{180}]$

Formula sheet available during quizzes at CBTF