I chose to begin my unit of geometry with a lesson on comparing angle types. Because students will be defining different shapes based on attributes including angles, this lesson is important to their success in the rest of the unit. While the students will not be using protractors for this lesson, they could be used if your students are ready for the more advanced measuring. During this lesson the students use index cards as the tool for comparing angles.
Because this lesson focuses on new vocabulary terms, I begin by providing visual examples of the the three types of angles. I draw these mathematical representations of an acute, obtuse, and right angle. I choose to make the examples similar to what will be seen on a standardized test, and later the students will be looking for real world examples. After the three visual examples are shown and labeled, I have the students begin to record these examples and words on their own index card. Then, I begin a class discussion about these types of angles.
The focus of discussion includes classifying the angles as small, medium, and large. I also have the students rotate their cards and look at the angles from different orientations or directions. Many of the students will quickly realize that the acute angle will look like a capital letter A. This is one of the first connections I make with them to help them remember the new vocabulary term of acute looks like a letter A.
During the discussion one of my students said the obtuse angle looks like a chaise lounge chair. Because we live in the desert southwest, these chairs are very familiar to the students who swim regularly.
After this discussion, I explain to the students their task of finding different examples in the classroom of the different types of angles. I ask questions including, "Which one do you think will be the easiest to find? Why?" Which one do you think will be the most difficult to find? Why?"
Students are given the task of locating two examples for each of the three types of angles. Students record the name of the item and trace or draw the visual example of the angle. Students have the option to use any item within the classroom. I encourage the students to find different examples from other students. Increasing the variety of items will make the activity more interesting for everyone.
During this activity I am asking students to describe and explain their thinking as it is occurring. In the video below, I asked students to describe why one angle of a triangle showed an obtuse angle, and another student saw it as a right angle, and there was also an acute angle as well.
This is the example of how these different angles exist, and people can look at them differently. It is interesting how students focused on locating the angle they needed for their own list, but also were able to explain their thinking to another student about the angle they focused on.
To close this lesson, the students discussed and explained their examples with their team. These discussion included finding as many different examples as they could. I feel it is important for the students to have these focused math conversations because it gives the students the chance to use the new vocabulary terms in a meaningful context. Here one students includes a written explanation during the discussion with a number line.
At the completion of this lesson, I have the students save their index cards for use in the future as needed with other lessons on shapes.