# The Naked Scientists Forum

### Author Topic: What governs the speed of rain running down a sloped window?  (Read 2662 times)

• Neilep Level Member
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##### What governs the speed of rain running down a sloped window?
« on: 04/08/2009 23:00:22 »
Watching the ever increasing rain rolling down my sloped glass conservatory roof, I wondered about the equations for the speed of the raindrops track. As the drops went down the glass they bumped into more raindrops and their speed increased. I was staggered by the amount of science going on above my head. I realised a lot of different equations could be used to predict the speed of the raindrops but wondered if anyone had ever done work on this before? Anyone seen anything?

[MOD EDIT = PLEASE PHRASE YOUR POST TITLES AS QUESTIONS, IN LINE WITH FORUM POLICY. THANKS. CHRIS SMITH]
« Last Edit: 08/08/2009 22:20:27 by chris »

#### syhprum

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##### Re: What governs the speed of rain running down a sloped window?
« Reply #1 on: 07/08/2009 21:46:27 »
This could well be a research project that earns an Ig-Nobel prize
« Last Edit: 07/08/2009 22:00:11 by syhprum »

• Neilep Level Member
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##### Re: What governs the speed of rain running down a sloped window?
« Reply #2 on: 07/08/2009 22:04:56 »

#### Soul Surfer

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• keep banging the rocks together
##### Re: What governs the speed of rain running down a sloped window?
« Reply #3 on: 08/08/2009 08:54:26 »
I have always been fascinated by that effect ever since I was a child it is a balance between the surface tension effect of the clean rainwater against the surface of the window  which tends to anchor the water to the surface in blobs and the force of gravity which pulls the blobs down.  If you put a tiny smear of detergent (washing up liquid) on the window which reduces the surface tension the pattern is very different.

• Neilep Level Member
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##### Re: What governs the speed of rain running down a sloped window?
« Reply #4 on: 08/08/2009 17:55:28 »
So what about self cleaning windows then?

#### The Naked Scientists Forum

##### Re: What governs the speed of rain running down a sloped window?
« Reply #4 on: 08/08/2009 17:55:28 »