How Figure Surface Sq Inches Rod

[Carroll Courtney]

Guys I am terrible when it comes to numbers, I did find a calculator for this that came up with 29" but I could not find an example. So I have a aluminum rod that has a 1" dia by 9" long so how would I go about how to figure the surface square inches? If you could give and example plus a formula that would help me understand.
I took one of those cloth tape measure and wrap it around the rod came up with almost 3" dia. then multiply that by 9 and I come up with 27 square inches. Trying to teach myself how to anodize aluminum which I also have to figure how many sq ins surface to setup the power supply.Thanks guys

[Lee Schierer]

The formula for the surface area of a cylinder is: Area = PI x diameter x length In your case 3.1415 x 1 x 9 = 28.2735 square inches

The area for one end is: Area = PI x radius x radius In your case: Area = 3.1415 x .5 x.5 = .785375 square inches

Total surface area of your cylinder is 28.2735 + .785375 + .785375 = 28.84425 square inches

[Perry Hilbert Jr]

I was always pretty good at Geometry and I am amazed at how often I use what I learned back in 10th grade 50 years ago. Knew a fellow that was in charge of ordering materials for commercial construction for a very large company. There were 8 or 10 guys who did the same job, but every time there was a structure with sweeping curves, the job landed on his desk because the others couldn't figure the surface areas. I would have thought there were some simple reference books for estimators to use for that stuff.

[Tom Stenzel]

The formula for the surface area of a cylinder is: Area = PI x diameter x length In your case 3.1415 x 1 x 9 = 28.2735 square inches

The area for one end is: Area = PI x radius x radius In your case: Area = 3.1415 x .5 x.5 = .785375 square inches

Total surface area of your cylinder is 28.2735 + .785375 + .785375 = 28.84425 square inches

Lee, you got it all correct. Then made a typo when you posted. The correct answer is 29.84425 square inches.

It happens.

-Tom

[John K Jordan]

Guys I am terrible when it comes to numbers, I did find a calculator for this that came up with 29" but I could not find an example. So I have a aluminum rod that has a 1" dia by 9" long so how would I go about how to figure the surface square inches? If you could give and example plus a formula that would help me understand.
I took one of those cloth tape measure and wrap it around the rod came up with almost 3" dia. then multiply that by 9 and I come up with 27 square inches. Trying to teach myself how to anodize aluminum which I also have to figure how many sq ins surface to setup the power supply.Thanks guys

Give a man a fish and you feed him for today....

There are zillions of web sites with clear explanations with good diagrams and formulas for area, volume, etc. For example google "surface areas of geometric shapes" and you'll find sites like this: http://www.math.com/tables/geometry/surfareas.htm

Same thing if you need to calculate angles or use angles to find linear dimensions, or motions and force. And conversions! Some will give you calculators and you can simply plug in values without messing with the formulas and risking a calculation error.

For example, want to estimate the wet weight of a log of a certain species? http://www.woodweb.com/cgi-bin/calculators/calc.pl?calculator=log_weight

I can remember most of the formulas and the trig, but I look it up when needed. Mister Internet is so helpful these days. I seldom reach for my math and physics text books or reference books. Or encyclopedia or dictionary.

JKJ

[Tom Bender]

Carroll
Your instincts were good but your measuring was a bit off, probably close enough. Pi is about the most famous and useful of all the non counting numbers. You might just tuck it in your memory for future use.