Naked Science Forum

General Science => General Science => Topic started by: Jonathan Shapiro on 01/05/2008 20:53:32

Title: Does waste reach terminal velocity on its way down to the sewers?
Post by: Jonathan Shapiro on 01/05/2008 20:53:32

Jonathan Shapiro asked the Naked Scientists:
Sorry about this.

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?

Title: Does waste reach terminal velocity on its way down to the sewers?
Post by: ukmicky on 01/05/2008 23:23:19

I doubt the poo's journey is straight down so no probably not.

Title: Does waste reach terminal velocity on its way down to the sewers?
Post by: another_someone 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?

Title: Does waste reach terminal velocity on its way down to the sewers?
Post by: turnipsock 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?

Title: Does waste reach terminal velocity on its way down to the sewers?
Post by: JimBob 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.

Title: Does waste reach terminal velocity on its way down to the sewers?
Post by: neilep on 02/05/2008 01:58:01

Quote from: Jonathan Shapiro on 01/05/2008 20:53:32

Jonathan Shapiro asked the Naked Scientists:
Sorry about this.

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 !!

Title: Does waste reach terminal velocity on its way down to the sewers?
Post by: chris on 02/05/2008 10:27:17

Quote from: JimBob on 02/05/2008 01:11:09

It will be turbulent flow.

turbulent?

"turdulent" more like.

Title: Does waste reach terminal velocity on its way down to the sewers?
Post by: lyner 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.

Title: Does waste reach terminal velocity on its way down to the sewers?
Post by: JimBob on 03/05/2008 01:45:55

Quote from: sophiecentaur 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.

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.

Title: Does waste reach terminal velocity on its way down to the sewers?
Post by: science_guy on 04/05/2008 22:14:50

Quote from: chris on 02/05/2008 10:27:17

Quote from: JimBob on 02/05/2008 01:11:09

It will be turbulent flow.

turbulent?

"turdulent" more like.

 [xx(] [:o] [:D] [:D]

that just about sums it up