# The Naked Scientists Forum

### Author Topic: Why is a hollow pipe stronger than a solid one?  (Read 27916 times)

#### yor_on

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##### Why is a hollow pipe stronger than a solid one?
« Reply #25 on: 13/01/2011 02:32:09 »
Naah, looking at it again it looks easily compressed as the joints will take all the pressure. That is the two at the middle. If you look at it as a flow the flow will separate at the top, run down to the middle but, well there, find no easy way to follow the 'structure' . That should mean that the 'forces' will accumulate at those two joints.

Does that make better sense.
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This message is brought to you by the coffee drinkers association, now in full flow.
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It is not round. Da*n it :) In a round pipe the forces will have no 'grip'. they will have to spread over the whole surface, maximizing the pipes strength per volume and mass of material. And this have to be true. Or I will ...

Drink more coffee.

Heh.
« Last Edit: 13/01/2011 02:40:17 by yor_on »

#### Geezer

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##### Why is a hollow pipe stronger than a solid one?
« Reply #26 on: 13/01/2011 02:44:11 »
Yup! The top and bottom right angles wil tend towards a straight line, while the right and left ones will close up. If you add a horizontal or vertical member to convert the square into two triangles, it will be able to resist bending much better.

#### yor_on

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##### Why is a hollow pipe stronger than a solid one?
« Reply #27 on: 13/01/2011 02:47:23 »
You know what, this goes back to a question I have. Would you agree to that a circle can be seen as an infinite collection of 'straight lines' slightly angled against each other?

If you do look at the pipe that way you could call each 'thought up' angle a 'joint' and then see that as they are so many and following each other so smoothly they will all share that 'force' applied at the pipe. And so the force becomes 'evened out' over the whole surface. And it also means that with a round pipe, when it 'compress' the force that does so will have to start at the sides of the pipe.

Yep..? :)

No, I'm sure I'm right here..

#### yor_on

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##### Why is a hollow pipe stronger than a solid one?
« Reply #28 on: 13/01/2011 02:53:11 »
Heh, we made a pretty good intuitive picture of it here, didn't we Geezer? Tout sweet as the Froggies say. And stop throwing things at me :)
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"And so the force becomes 'evened out' over the whole surface." is not perfectly correct as the most pressure per joint will be at the middle, but as a flow it will find its way around easier than when meeting that 90 degree turn you gave in your rotated square pipe, as I think of it. Seems you need to think of it both as a flow and then of the geometry as well as of the 'force direction'.

All as i see it :)
« Last Edit: 13/01/2011 02:57:50 by yor_on »

#### Geezer

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##### Why is a hollow pipe stronger than a solid one?
« Reply #29 on: 13/01/2011 03:02:52 »
You know what, this goes back to a question I have. Would you agree to that a circle can be seen as an infinite collection of 'straight lines' slightly angled against each other?

If you do look at the pipe that way you could call each 'thought up' angle a 'joint' and then see that as they are so many and following each other so smoothly they will all share that 'force' applied at the pipe. And so the force becomes 'evened out' over the whole surface. And it also means that with a round pipe, when it 'compress' the force that does so will have to start at the sides of the pipe.

Yep..? :)

No, I'm sure I'm right here..

Yes. I think that's quite right. The diamond shape on the right is a very crude approximation to the pipe. The diamond will only hold up as long as the angles don't alter, but there is a lot of force trying to alter the angles.

With the square on the left, there is no force tending to alter the angles.

The round pipe will only hold up as long as the material it is made from is rigid enough to maintain it's curvature (which can be considered an infinite number of angles).

#### yor_on

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##### Why is a hollow pipe stronger than a solid one?
« Reply #30 on: 13/01/2011 03:07:52 »
I think this one should be a sticky :)

The next endeavor Geezer, will be to apply it on SpaceTime :)
Let's make a wiki ::))

ahem :)
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And to make it perfectly correct.

When you look at a pipe you would do well to both consider it consisting of an infinity of angles (joints) and also 'split in the middle'.

Split in the middle because any force applied will according to Newton meet a reaction in the opposite direction. so when you put pressure on the top of that pipe resting, let us say, on the ground (for the visual effect) then the 'reaction' will be an equal force meeting it from the earth, both applying the most pressure in the middle.

If the pipe is freely mounted in the air you still will need a foundation for it, ending in the ground somewhere, so the same reasoning should apply, I think? Maybe it will differ slightly though depending on the 'joints' connected to that piece of pipe we see the pressure applied on.
« Last Edit: 13/01/2011 03:17:32 by yor_on »

#### Geezer

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##### Why is a hollow pipe stronger than a solid one?
« Reply #31 on: 13/01/2011 03:18:28 »
It would not totally surprise me if there is some connection here with curvature and stress in space, but I haven't the faintest idea how

#### yor_on

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##### Why is a hollow pipe stronger than a solid one?
« Reply #32 on: 13/01/2011 03:36:47 »
I reckon you're perfectly right Geezer.

We only need to find out where SpaceTime is mounted.
That is, where is the foundation?

Then we can follow the stress tension all from there. I will start immediately. Me and me pal Jules will build ourselves one of those bullets and fly of in search. It can't be that big, can it?

SpaceTime?
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But seriously, I do think you're right.
And the 'foundation' will be a interesting thing to see.
If we find it.
« Last Edit: 13/01/2011 03:40:13 by yor_on »

#### damocles

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##### Re: Why is a hollow pipe stronger than a solid one?
« Reply #33 on: 03/05/2013 07:14:02 »
PS our builders use a metric foot what ever that might be!

30 cm it is: just enough to save 1% and to make joints in replacement timber very loose!

In Australia we are almost completely across to the metric system (SI) by now, but there are a few glaring anomalies!
Ceramicists write their recipes in "gram per pint".

#### The Naked Scientists Forum

##### Re: Why is a hollow pipe stronger than a solid one?
« Reply #33 on: 03/05/2013 07:14:02 »