Classifying Shapes by Sides, Corners, and Lengths

Khan Academy

This engaging math video features a dialogue between Sal and his high-pitched relative, Cousin Fal, who needs help organizing a collection of colorful 2D shapes. The narrative guides viewers through the fundamental process of geometric classification by teaching them to observe and count specific attributes, such as the number of sides and corners (vertices) for each shape. Key themes include identifying geometric properties, counting to four, and comparing lengths. The video covers various shapes including quadrilaterals (parallelograms, rhombuses, squares), triangles, and curved shapes (ovals), explicitly demonstrating that not all shapes have straight sides or corners. It advances to a second level of classification by asking students to determine if a shape has sides of equal length. This resource is highly valuable for early elementary classrooms introducing geometry. It models mathematical thinking by asking questions and verifying answers through visual proof—tracing sides and circling corners. It helps students move beyond simply naming shapes (e.g., "that's a square") to defining them by their attributes (e.g., "it has 4 equal sides and 4 corners").