[u][size=200][b]Sphere Facts[/b][br][/size][/u][br][img]http://www.mathsisfun.com/geometry/images/sphere-radius.svg[/img][br][b]Notice these interesting things:[/b][br][list][*]It is perfectly symmetrical[/*][*]All points on the surface are the [br]same distance [b]"r"[/b] from the center[/*][*]It has [b]no[/b] edges or [br]vertices (corners)[/*][*]It has one [b]surface[/b] [br](not a "face" as it isn't flat)[/*][/list][br] [img width=304,height=299]http://www.mathsisfun.com/geometry/images/sphere-glass.jpg[/img][i][br][/i][i]Glass Sphere[/i]. [br]Balls and marbles are shaped like spheres.[br][br][b][u][size=200]Largest Volume for Smallest Surface:[br][/size][/u][/b][br]Of all the shapes, a sphere has the smallest surface area for a volume. Or put another way it can contain the greatest volume for a fixed surface area.[br][br][b][u]Example:[/u][/b] if you blow up a balloon it naturally forms a sphere because it is trying to hold as much air as possible with as small a surface as possible[br] [br][b][u][size=200]In Nature[br][img width=200,height=193]http://www.mathsisfun.com/geometry/images/bubble.jpg[/img][br][/size][/u][/b]The sphere appears in nature when a surface wants to be as small as possible. [b]Examples[/b] include bubbles and water drops. Can you think of more?[br][br][table][tr][td][b][u]The Earth:[br][/u][/b]The Planet Earth, our home, is [i]nearly[/i] a sphere, except that it is squashed a little at the poles.[br][/td][td][img width=162,height=162]http://www.mathsisfun.com/geometry/images/planet-earth.jpg[/img][/td][td][br]It is a [b]spheroid[/b], which means it just misses out on being a sphere because it isn't perfect in one direction (in the Earth's case: North-South)[/td][/tr][/table][br][b][u][size=200]Volume and Surface Area[/size][/u][/b][br][img]http://www.mathsisfun.com/geometry/images/sphere-radius.svg[/img][br][b]Surface Area = 4 × [i]π[/i] × r[sup]2[br][/sup][/b][br][b][u]Example:[/u][/b] r = 5[br][br]Surface Area= 4 × π × r[sup]2[/sup][br]    = 4 × π × 5[sup]2[/sup][br]    = 4 × π × 25[br]    = 100 π[br]    ≈ 314[br] [br][b]Volume = (4/3) × [i]π[/i] × r[sup]3[br][/sup][/b][br][b][u]Example:[/u][/b] r = 5[br][br]Volume= (4/3) × π × r[sup]3[/sup][br]   = (4/3) × π × 5[sup]3[/sup][br]   = (4/3) × π × 125[br]   ≈ 524[br][br][size=200][b][u]Hemisphere[br][/u][/b][br][/size][img width=221,height=287]http://www.mathsisfun.com/geometry/images/hemisphere.jpg[/img][br]A hemisphere is an exact half of a sphere.[br][br][b][u][size=200]Other Cool Spheres[br][/size][/u][/b][br][img width=301,height=250]http://www.mathsisfun.com/geometry/images/sphere-crystal.jpg[/img][img width=190,height=192]http://www.mathsisfun.com/geometry/images/marble.jpg[/img][br][table][tr][td][img width=173,height=178]http://www.mathsisfun.com/geometry/images/sphere-jade.jpg[/img][/td][td][img width=171,height=178]http://www.mathsisfun.com/geometry/images/sphere-check.jpg[/img][/td][/tr][tr][td][img width=166,height=178]http://www.mathsisfun.com/geometry/images/sphere-dark.jpg[/img][/td][td][img width=171,height=178]http://www.mathsisfun.com/geometry/images/sphere-brass.jpg[/img][br][br][/td][/tr][/table]