Area of a Sphere

Grade 9s are working on understanding how to calculate surface are and volume these days. Today’s activity shows how to calculate the surface area of a sphere.

We measured an orange, and drew 5 or 6 circles with the same diameter.

We then peeled the orange and filled the circles, like a jigsaw puzzle.

We can always fill 4 circles with the peels. We know already how to calculate the surface area of a circle, A=(pi)(r)^2, so the surface area of a sphere is A=4(pi)(r)^2.