ALL ANIMATIONS / Cylinder from Sphere
The surface area of a sphere is opened up to illustrate how the formula surface area = 4 Π r2 can be understood. The animation starts with a lined sphere. The upper and lower hemisphere skins then open out to form the sphere's enclosing cylinder. This cylinder unwraps to demonstrate how its circumference (2Πr) and its height (2r) combine to give 4Πr2.
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