Fix some mistakes

mechanical/mmme1028_statics.md

@@ -42,6 +42,7 @@ Can be found here [here](./lecture_exercises/mmme1028_l1.2_exercises_2021-10-04.
 
 <details>
 <summary>
+
 ### Example
 
 Determine force $F$ and $x$ so that the body is in equilibrium.
@@ -506,13 +507,13 @@ $$ \epsilon_x = \frac {\Delta L}{L_0} $$
 $$ \epsilon_y = \frac {\Delta w}{w_0} $$
 $$ \epsilon_z = \frac {\Delta t}{t_0} $$
 
-Poissons' ratio, $\nu$ (the greek letter _nu_, not v), is the ratio of lateral strain to axial
+Poisson's ratio, $\nu$ (the greek letter _nu_, not v), is the ratio of lateral strain to axial
 strain:
 
 $$ \nu = \frac{\epsilon_y}{\epsilon_x} = \frac{\epsilon_z}{\epsilon_x} $$
 
 <details>
-</summary>
+<summary>
 
 #### Example 1