http://www.ck12.org Chapter 11. Surface Area and Volume
Example 1:The circumference of a sphere is 26πf eet. What is the radius of the sphere?
Solution:The circumference is referring to the circumference of a great circle. UseC= 2 πr.
2 πr= 26 π
r= 13 f t.Surface Area of a Sphere
One way to find the formula for the surface area of a sphere is to look at a baseball. We can bestapproximatethe
cover of the baseball by 4 circles. The area of a circle isπr^2 , so the surface area of a sphere is 4πr^2. While the covers
of a baseball are not four perfect circles, they are stretched and skewed.
Another way to show the surface area of a sphere is to watch the link by Russell Knightley, http://www.rkm.com.a
u/ANIMATIONS/animation-Sphere-Surface-Area-Derivation.html. It is a great visual interpretation of the formula.
Surface Area of a Sphere:Ifris the radius, then the surface area of a sphere isSA= 4 πr^2.
Example 2:Find the surface area of a sphere with a radius of 14 feet.
Solution:Use the formula,r= 14 f t.
SA= 4 π( 14 )^2
= 784 πf t^2Example 3:Find the surface area of the figure below.