Okay, I need a quick answer pls! I am reciting this example from a Tafe construction book:
To calculate the surface area of a cylinder having a height of 2.100m and a base radius of 850mm:
Area= (I cant find pie symbol on my computer!) (pie x radius squared) + (2x pie x radius x height)
= (3.142x 0.723x 2) + (2x 3.142x 0.850 x 2.100)
= 4.540 + 11.217= 15.757 m 2
Now… I get the formula. But how where the hell does the "0.723" as the "radius squared" come from??
Can anyone help by tonight pls? Or…. an easier way (PLEASE??) to work out the volume of a cylinder?
(Eg: How much concrete is needed for 2 colums 600mm in diametre x 4.95 high??
The area of a circle from memory is;
A= pi x R squared or; area equals pi x radius squared.Then, multiply this by the depth of the cylinder to get the volume – I think.
It's been a hundred years since I was in school.
Misty1 wrote:Okay, I need a quick answer pls! I am reciting this example from a Tafe construction book:
To calculate the surface area of a cylinder having a height of 2.100m and a base radius of 850mm:
Area= (I cant find pie symbol on my computer!) (pie x radius squared) + (2x pie x radius x height)
= (3.142x 0.723x 2) + (2x 3.142x 0.850 x 2.100)
= 4.540 + 11.217= 15.757 m 2
Now… I get the formula. But how where the hell does the "0.723" as the "radius squared" come from??
Can anyone help by tonight pls? Or…. an easier way (PLEASE??) to work out the volume of a cylinder?
(Eg: How much concrete is needed for 2 colums 600mm in diametre x 4.95 high??
Hi Misty,
Its been a long time since I've looked at any maths, but here is what I think. The volume of a cylinder is end area x height. The end area of a circle is pi x (radius squared) which is 3.142 x radius x radius.
In your example the radius is 850 mm, which is 0.85 meters so the radius squared is 0.85 x 0.85 = 0.7225. Rounded up this is the 0.723 in your example.
I think For a 600mm by 4.95 m column the formula would be:
(3.142 x (0.6 x 0.6)) x 4.95
= (3.142 x 0.36) x 4.95
= (1.13112 x 4.95)
= 5.60 cubic meters for each column
That is for the volume of a cylinder, to calculate the surface area which you have taked about in your question is a different thing. For that you need the area of the ends calculated as pi x (radius squared) [x 2 if you want to count both ends]. To get the surface area of the walls of the cylinder you need the circumference of the end x the height of the cylinder. The circumferance is pi x diameter ( or pi x radius x 2).
The volume of a cylinder is measured in cubic meters and the surface area is calculated in square meters.
Hope this makes sense.
Misty,
.723 is the radius squared!
It has been converted from mm to metres.
ie. it is 0.85 squared.Hope this is not too late.
Thanks everyone. It's funny, I've asked 3 "whizzes" today, and all 3 had a different opinion…….
Take the average of all 3
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