Angles are an integral part of geometry, a subject that envelopes the material world around people. Learning about angles gives better insights as to how ordinary objects work. In architecture, for example, an understanding of angles allows a builder to construct a structure that will not fall apart. In sports, angles figure into swings or the strategic placement of players, which might spell a win or a loss for a team. The basic types of angles are straight, right, acute and obtuse. Obtuse, which also means “blunt,” angles are anything in between a straight angle (180°) and a right angle (90°). They are found in many real-life objects around you.

Many roof trusses show a visible obtuse angle. The ordinary house has a low ridge roof and the peak of the roof creates an obtuse angle. This is the most common type of truss in many areas, mostly due to its practicality. Right and acute angle trusses create an unusual shape compared to that of an obtuse angle.

Googie, populuxe or doo-wop architecture is a type of modern novelty architecture that originated in California some time in the 1940s. This style is still evident in many buildings in Los Angeles. Its identifying features include illuminated plastic panels, plate glass windows, elaborate signs, inverted triangles and cantilevered structures. Many Googie buildings sport a roof that is close to 2/3 of an upside down obtuse triangle.

Many household items display obtuse angles. Bay windows, for instance, have corner angles that are either 135 or 150 degrees -- if they have a polygonal plan. Recliners in their reclined form show an obtuse angle between the backrest and the seat. The same is true for chaise lounges. In the kitchen, a folding dish rack when open and holding dishes also forms an obtuse angle.

Tempered glass is produced by first heating a normal sheet of glass so that it becomes soft and then quickly dousing it with jets of very cold air. This process redistributes compression stress on the surfaces while keeping tensile stress toward the center. The process makes tempered glass much stronger than ordinary glass. When broken, tempered glass comes apart in fragments with obtuse angles, which are safer than the usual shards and smithereens of broken glass.

The teacher doesn’t have to look very far for examples of obtuse angles. Three of the letters in the English alphabet feature obtuse angles. The letters X, K and Y all have obtuse angles that are not noticeable right away. If students look carefully, they’ll find obtuse angles on both sides of X and Y and on the right side of K. Other objects that depict obtuse angles are a book (when opened to certain angles), a pair of scissors, and a door opened wide.