| 1 | It is an acute angle. | |
| 2 | The ramp sits at an acute angle to deflect the intake airstream from the longitudinal direction. | |
| 3 | Open book - Same as a dihedral or inside corner. Two panes of rock join in an acute or obtuse corner that faces left or right. | |
| 4 | Right triangle: One of the three angles is a right angle. The other two are acute angles. | |
| 5 | Angles of less than 90 degrees are called acute angles. |