Surface area is a such a fun topic to explore in the middle school math classroom! To really understand what surface area means, students need to interact with actual threedimensional objects. Before we talk about the math formulas or how to calculate, we spend time discovering how to find surface area in our own ways.
I give students everyday items to work with. Typically, we use product boxes (rectangular prisms) with different dimensions, and I ask the students to visualize and then draw what the boxes would look like if they were taken apart and laid flat. Most students take about 5 minutes to complete their drawings, depending on how detailed they choose to be, and for the most part, they do a very good job drawing the nets of the boxes. Next, I have them spend a few minutes comparing their nets with group members, deciding whether those nets are reasonable representations of the object (even if they are drawn a little differently), and determining whether anyone appeared to be missing anything (some students will draw only five sides, and their group members are able to help them figure out what's missing).
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Although we're trying to get through quite a bit of material before our state testing, we took some time today to explore triangles. I'm sure many of you may have done this exploration, but it was quick and fun, so I thought I'd share:) We explored the idea that the sum of the two smaller sides of a triangle must be greater than the longest side. I cut straws of three different lengths, and asked students (in groups) to use the straws to make a triangle.
In my first math class, I used straws that were cut to 2 inches, 3 inches, and 5 inches. These lengths, using straws, made it almost possible to make a triangle, even though it shouldn't have been possible. So, I had to insist that their straw ends be lined up perfectly. I wanted to use 3, 5 and 2 inches to show that even these dimensions won't make a triangle, because the sum is equal to the longest side, not longer than it. So, after understanding how precise they had to be and that they couldn't leave segment parts sticking out of the end of the triangle, they came to the conclusion that it couldn't be done. Next I gave the groups a new set of straws that were cut to 3 inches, 3 inches, 5 inches. In this case, they were excited to make their triangles in about 30 seconds! We then discussed why the 3, 2, 5 didn't work and worked our way to "creating" the rule.
For my next classes, I trimmed the 3 inch straws to 2 inches, so that my next classes would have more difficulty getting the ends to meet. It was so funny to hear their comments  "This doesn't work," "Is this a trick question?" "This is impossible!" And then, their excitement when they made the 3, 3, 5 triangle  "We did it first!"
For my next classes, I trimmed the 3 inch straws to 2 inches, so that my next classes would have more difficulty getting the ends to meet. It was so funny to hear their comments  "This doesn't work," "Is this a trick question?" "This is impossible!" And then, their excitement when they made the 3, 3, 5 triangle  "We did it first!" I think (hope!) that they understood the concept....we'll see tomorrow when we go over their homework:) 
AuthorHi, I'm Ellie! I've been in education for 25 years, teaching all subject areas at both the elementary and middle school levels. Categories
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