Many of my past and current Geometry students have had trouble memorizing the formulas for volume and surface area. Traditionally, teachers have asked students to memorize all of the formuals below.
| Name | Lateral Area | Surface Area | Volume |
|---|---|---|---|
| Prism | L.A. = Ph | S=L.A. + 2B = Ph + 2B |
V = Bh |
| Cylinder | L.A. = Ph = Ch = 2πrh |
S.A. = L.A. + 2B = 2πr + 2πr² |
V = Bh = πr²h |
| Regular/Square Pyramid | L.A. = ½Pl | S.A. = L.A. + B = ½Pl + B |
V = ⅓Bh |
| Cone | L.A. = ½Pl = ½Cl = ½(2πr)l = πrl |
S.A. = L.A. + B = πrl + πr² |
V = ⅓Bh = ⅓πr²h |
| Sphere | S.A. = 2πrh = 2πr*2r = 4πr² |
V = 4/3πr³ |
This is a lot for anyone to remember. Our jobs as math teachers is to help students make connects between all of these formulas. The connections between them allow students to memorize very little and to generate these formulas based on their knowledge of how they are related. This also provides students with a much deeper understanding of the math.
Here are just a couple visual representations of some of these connections that I commonly share with my own students.
And in that vain, I created a Desmos graph that shows a visuallization of the connection between the latteral area of a cylinder and the surface area of a sphere. Click on the graph below to see the math behind it on Desmos.com.