One of the hardest Calculus topics for my students to visualize is rotating areas around an axis to create a solid. Fortunately, you can now create a great 3D representation of rotated solids using GeoGebra’s 3D app. Once you get the hang of it, it is quick and a heck of a lot easier than trying to draw them by hand!
Before I go any further, I want to give credit to Steve Phelps for posting a demo of this technique on his Twitter feed. If you are a math teacher, you really should follow him @MathTechCoach. I have learned more cool tech tricks from him than anyone else online.
Here’s my screencast illustrating how to create your very own rotated solids:
FracTad's Fractopia 