# The Naked Scientists Forum

### Author Topic: Does waste reach terminal velocity on its way down to the sewers?  (Read 6393 times)

#### Jonathan Shapiro

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##### Does waste reach terminal velocity on its way down to the sewers?
« on: 01/05/2008 20:53:32 »
Jonathan Shapiro asked the Naked Scientists:

If you flush a No.2 from a loo on the 98th floor of a tower office block, does the missile-shaped deposit plummet straight down and smash into the bottom of the drain,leaving an incredible skid mark, or does it gently land to be wafted away by the water?
What do you think?

#### ukmicky

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##### Does waste reach terminal velocity on its way down to the sewers?
« Reply #1 on: 01/05/2008 23:23:19 »
I doubt the poo's journey is straight down so no probably not.

#### another_someone

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##### Does waste reach terminal velocity on its way down to the sewers?
« Reply #2 on: 01/05/2008 23:27:40 »
What is terminal velocity in this case?  Is not terminal velocity contextual, being that velocity where the frictional forces balance the gravitational forces, and so in this case, is it not merely that the frictional forces being greater, mean that terminal velocity is very much lower, and that lower terminal velocity is indeed reached?

#### turnipsock

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##### Does waste reach terminal velocity on its way down to the sewers?
« Reply #3 on: 02/05/2008 00:11:33 »
When you stay in a hotel, why is there always somebody on the top floor that insists on flushing the toilet in the middle of the night? Is it the same person?

#### JimBob

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##### Does waste reach terminal velocity on its way down to the sewers?
« Reply #4 on: 02/05/2008 01:11:09 »
Most probably not. In order for to real terminal velocity in a pipe the fluid, or fluid mixture in this case, must be in a state called laminar flow. That means there is no turbulence. No sewer pipe with a no 2 is going to have laminar flow. It will be turbulent flow.

For the definitions of laminar and turbulent flow see:

http://en.wikipedia.org/wiki/Laminar_flow  - the picture of smoke on this page shows both laminar and turbulent flow.

#### neilep

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##### Does waste reach terminal velocity on its way down to the sewers?
« Reply #5 on: 02/05/2008 01:58:01 »
Jonathan Shapiro asked the Naked Scientists:

If you flush a No.2 from a loo on the 98th floor of a tower office block, does the missile-shaped deposit plummet straight down and smash into the bottom of the drain,leaving an incredible skid mark, or does it gently land to be wafted away by the water?
What do you think?

I luff the idea of my poo travelling at a 120 mph !!

Please let it be yes !!

#### chris

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##### Does waste reach terminal velocity on its way down to the sewers?
« Reply #6 on: 02/05/2008 10:27:17 »
It will be turbulent flow.

turbulent?

"turdulent" more like.

#### lyner

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##### Does waste reach terminal velocity on its way down to the sewers?
« Reply #7 on: 02/05/2008 13:10:05 »
Even if it's going down a slope it will still reach 'A' terminal velocity i.e. it won't go any faster.
It's bound to touch the sides of a 'vertical run', in any case, so it won't end up very fast.
« Last Edit: 02/05/2008 13:12:54 by sophiecentaur »

#### JimBob

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##### Does waste reach terminal velocity on its way down to the sewers?
« Reply #8 on: 03/05/2008 01:45:55 »
Even if it's going down a slope it will still reach 'A' terminal velocity i.e. it won't go any faster.
It's bound to touch the sides of a 'vertical run', in any case, so it won't end up very fast.

I was considering terminal velocity as the maximum velocity gravity could produce, not th maximum velocity that flow through a pipe would produce.

It doesn't make any difference - it is still a dirty business.

#### science_guy

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##### Does waste reach terminal velocity on its way down to the sewers?
« Reply #9 on: 04/05/2008 22:14:50 »
It will be turbulent flow.

turbulent?

"turdulent" more like.

[xx(]

that just about sums it up

#### The Naked Scientists Forum

##### Does waste reach terminal velocity on its way down to the sewers?
« Reply #9 on: 04/05/2008 22:14:50 »