Subject: cylinders or shafts

Name: JIm Campbell
Who is asking: Other
Level: All

Question:
I am going to cover the outside of a shaft with some material. How do I figure the square inches of the outside surface of the shaft? Shaft is 6" in diameter and 24" long

The same way that you would find the area, in square inches, of the label on a soup can. Slice the label vertically and roll it out flat. You get a rectangle with height the height of the label and length the circumference of the can. The circumference of a circle is 2 pi times the radius, so the area of the label (surface area of the "shaft") is 2 pi times (the radius) times (the height). We usually write this 2 pi r h