Hollow Cylinder volume

**mybrohshi5** · February 17th 2010, 05:04 PM

Does anyone know the equation to find the volume of the solid material that makes up a hollow cylinder.

I know the height, outer diameter, and thickness.

What equation will give me the volume of just the material that makes up the hollow cylinder?

Thank you

**pickslides** · February 17th 2010, 05:30 PM

Volume for a cylinder is $V = \pi r^2h$

The volume you are taking about is the inner volume of your shape subtracted from the outer volume.

You just need to find the two diameters/radui (outer and inner) to solve this problem. The Thickness should give you a good hint.

So $V = \pi r_\text{outer}^2h - \pi r_\text{inner}^2h$

**mybrohshi5** · February 17th 2010, 05:36 PM

That is how i did it but my teacher gave me an equation that is giving me different answers and im wondering if maybe i wrote the equation down wrong.

This is for my physics lab and my teacher gave me this equation:

[ 2(pi)(D)(T) - (pi)(T^2) ] x H

This isnt giving me the same number though compared to finding it the way you mentioned.

And the number isnt just a little different its like twice as large using that equation compared to if i find it the way you mentioned.

**pickslides** · February 17th 2010, 05:38 PM

What are your values for height thickness and outer diameter?

(As mentioned in the first post)

**Diagonal** · February 17th 2010, 05:43 PM

Originally Posted by mybrohshi5

Does anyone know the equation to find the volume of the solid material that makes up a hollow cylinder.

I know the height, outer diameter, and thickness.

What equation will give me the volume of just the material that makes up the hollow cylinder?

Thank you

You need the "mean" distance. Subtract the thickness from the outside diameter to get the inside diameter. If the outer radius is D/2, the thickness, T, then the inner radius will be (D/2)-T. Find the area of the annulus [ring] by finding the outside area and subtracting the inside circle area. Multiply by the length [height]. If you want to include the bottom, you'll have a circle of radius (D/2)-T. Multiply that by the thickness, T, for its volume.

**mybrohshi5** · February 17th 2010, 05:49 PM

Originally Posted by pickslides

What are your values for height thickness and outer diameter?

(As mentioned in the first post)

Height = 12.729 cm

Diameter (outer) = 8.623 cm

Thickness = 0.509 cm

I get 342.4 cm^3 using the equation my teacher gave me but when i do it the way you meantioned i get 662.897 which is actually double not half like i thought.

**pickslides** · February 17th 2010, 05:58 PM

$<br /> V =\pi r_\text{outer}^2h - \pi r_\text{inner}^2h= \pi \times 4.3115^2\times 12.729 - \pi \times 4.057^2\times 12.729 = \dots<br />$

**mybrohshi5** · February 17th 2010, 06:05 PM

Originally Posted by pickslides

$<br /> V =\pi r_\text{outer}^2h - \pi r_\text{inner}^2h= \pi \times 4.3115^2\times 12.729 - \pi \times 4.057^2\times 12.729 = \dots<br />$

opps i was using diameter when i got the 600 number.

the V = 85.59

the 12.729 was supposed to be 12.792

but anyways why is this so much smaller than what i get using the equation my teacher gave me? Do you think i wrote it down wrong or can you see anything wrong with it that would fix my problem?

Thank you

**pickslides** · February 17th 2010, 06:14 PM

Originally Posted by mybrohshi5

but anyways why is this so much smaller than what i get using the equation my teacher gave me? Do you think i wrote it down wrong
Thank you

Could be a reason.

**mybrohshi5** · February 17th 2010, 06:15 PM

HMMM ok well thank you for your help

**Diagonal** · February 17th 2010, 06:26 PM

File attached. Oops, missed a bracket.

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