Circles have a different


Circles have a different equation.  Remember that a radius is half the diameter of the circle.  An 8 inch circle has a 4 inch radius.  A 10 inch circle has a 5 inch radius.

Volume of a circle = 3.14 x radius x radius x height

So if we want an 8 inch circle that is 1/4 inch thick…

3.14 x 4.00 x 4.00 x 0.25 = 12.56 cubic inches

Again we have to convert those pesky inches to centimeters

12.56 cubic inches = 205.82 cubic centimeters

Now mulitpy by 2.5 just like with rectangles

205.82 x 2.5 = 514.55 grams  Tada!

Again, if you start with centimeters it is MUCH easier

3.14 x radius x radius x height x 2.5 = grams of glass needed

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