Khan Academy
Khan Academy: Parallel & Perpendicular Lines Intro
Learn the properties of parallel and perpendicular lines so that you can easily identify them. [2:08]
Khan Academy
Khan Academy: Classifying Shapes by Line and Angle Types
Explains how to classify 2D shapes based on the properties of their sides and angles. [2:15]
Shmoop University
Shmoop: Triangles
A video clip [2:09] using an everyday bag of chips to explain the different types of triangles.