Volume and Surface Area using Nets

I explained to my classes that today we would be reviewing the concept of volume.  I wanted to visually remind them about the formula and the fact that, in math, we are actually finding the number of cubes that will fill a 3-D figure.  I began by holding up a shoebox and placing inch cubes within.  I showed them them length (12 cubes) the width (7 cubes) and the height (4 cubes).  We found the volume (12 x 7 x 4 = 336) and I explained that we discovered that 336 inch cubes would fill the box.

Next, we took out the nets we had created last Thursday using the ordered pairs activity I had found on Teachers Pay Teachers.  We cut out the nets that made a cube and folded the 3-d figure keeping the grid on the outside so that we could count squares to find our length, width, and height.  Basing my lesson from a lesson on Runde's Room, I asked them to tell me the definition of volume (the amount of space inside an object) and I reminded them that we are filling the space with cubes.  Using this information, we found the volume of the cube.

Then we moved into surface area.  We defined surface area as the total area of the faces of a polyhedron (3-d figure).  Then I had them write an equation for finding Surface Area:

2[(l x w) + (l x h) + (w x h)]

Before finding the surface area, I felt that I needed to explain why we multiplied by 2.  So, I brought out the shoebox and explained that we would find the area of the top of the box, but I wondered if there was any other part of the box that would have the same measurement.  This really helped them to visualize how the formula worked.  We then found the surface area of the cube.  I chose not to use the formula for finding the surface area of a cube (SA = L x W x 6) because I felt one formula was enough!

All of this information is leading to our Angry Bird Project.  Students will need to know how to find surface area and volume to complete the project.  To see their projects and hear them discuss the math they they used, please be sure to attend our AWEsome Expo on Tuesday, May 26 from 5:30 - 7:00 p.m. in the Elementary Cafeteria.