๐ Archimedes map
๐ฏ A demonstration Helionโs concise and powerful graphic capabilities
๐ง Inspired by Archimedes map by Steve Trettel
๐ Why Is a Sphereโs Surface Area 4ฯrยฒ? Visual Proof, No Calculus
What am I looking at?
Section titled โWhat am I looking at?โFrom Why Is a Sphereโs Surface Area 4ฯrยฒ? Visual Proof, No Calculus:
Why is the surface area of a sphere exactly ? Archimedes found the answer over 2,000 years ago, with no calculus.
In this 2-minute visual proof, youโll see:
๐ Why the skin of a sphere covers exactly 4 circles of the same radius
๐ How Archimedes compared a sphere to a cylinder (a can) wrapped around it
๐ Why a patch of the sphere and its โshadowโ on the canโs wall have the same area: where one stretches, the other shrinks
๐งฎ Why the canโs wall is
Key idea: sphereโs skin = canโs wall, so they have the same area.
0:00 The orange and the paper circles 0:20 Archimedes and the can 0:40 Patch and shadow: stretched sideways, squeezed toward the pole 1:20 The canโs wall = 4ฯrยฒ 1:50 Why this equals 4 circles