# Rain drops

1. Jul 10, 2008

### moe7404

moe in wichita ks
how many drops are in 1 inch of rain on a 1 inch dia tube?
of course iam guessing that all rain drops are the same size, which most likely they are not. sounds the like this is going to have a lot averages in the answer.

2. Jul 10, 2008

### Redbelly98

Staff Emeritus
The answer comes down to: what is the volume of an average water drop? I don't know if there is a scientifically accepted, standard water-drop volume. You might try an online search and see what you can find.

The container volume is

$$\frac{\pi}{4} \ in^3 = 0.785 \ in^3 = 12.9 \ cm^3 = 12.9 \ ml$$

so to get the number of drops, divide the container volume by the average volume of a drop.

3. Jul 10, 2008

### moe7404

moe in wichita ks
thanks to redbelly98 for crunching some numbers, thats a big help.
the reason i am asking this Q is that i am thinking of making a different way to measure rain fall. my idea is have a square plexaglass box with a set beams going across two different ways, and count the number of broken beams in a certin length of time. what think? thanks for any help

4. Jul 11, 2008

### Hootenanny

Staff Emeritus
That would certainly give you a more accurate measure of how many rain drops fall, assuming of course that the 'mesh' of beams is sufficiently fine. However, I'm not sure that knowing how many raindrops fell in addition to the total volume of water would be more useful than simply measuring the total height of water.

I'm also intrigued as to why you would chose a cubic box over a cylindrical tube?

Last edited: Jul 11, 2008
5. Jul 11, 2008

### DaveC426913

Because his two sets of beams are perpendicular. He's making a square grid.

As Hoot points out, of what use to anyone is the number of raindrops? Surely the volume of water over time is the only relevant factor, or are you looking to offer this as a new feature in rainfall measurements?

BTW, how do you account for a raindrop breaking more than one beam (while still ensuring the grid's fine enough to not let any drops fall through the gaps)?

6. Jul 11, 2008

### gmax137

"I'm not sure that knowing how many raindrops fell in addition to the total volume of water would be more useful than simply measuring the total height of water."

"...of what use to anyone is the number of raindrops..."

maybe he doesn't want to empty the rain gage -

7. Jul 11, 2008

### Redbelly98

Staff Emeritus
Such a gauge would give you an "instantaneous" reading of the rainfall rate. It would also allow one to measure very small rainfalls such as 0.01".

Moe, rather than calculating the number of raindrops based on some assumed average volume, it would be better to calibrate the device after building it. Just test it against a standard raingauge, and see how many drops are counted vs. the height of the water in the gauge. This way, any systematic errors get accounted for, eg. what if only 90% of the drops are detected?

8. Jul 11, 2008

### Integral

Staff Emeritus
Rain drop size varies a LOT, in a mist the drops are tiny much less then a mm. In a drizzle they tend to vary but generally bigger then a mist but smaller then rain. When a major storm dumps the drops can be huge, several mm in dia. Not sure how you can use a drop count for tracking rainfall when there is so much variation.

9. Jul 11, 2008

### moe7404

moe in wichita ks
i thank you all for your ideas. my first idea was just to have a different way to measure rain fall. if it could be made to work its main advantage would be measuring would be done second by second, and not having a moving part. but you points are well taken, the main one being that rain drops are all kinds of sizes. i thank you all for your ideas. i realy love this site. thanks

10. Jul 11, 2008

### bassplayer142

You could get some piece of metal or plastic and when it rains pick up the water with an eyedropper. Or better yet get a very sensitive scale and measure weight as some drops fall on it. Then you can easily get volume through mass and density.

11. Jul 11, 2008

### DaveC426913

Huh. Now that's a new feature. :!!) The acme of rainfall measurement science today is only able to measure after-the-fact.

12. Jul 12, 2008

### RonL

My suggestion for finding the most common size for a drop of water, would be to have a flat surface (like the ceiling of a shower) if you use steam in the shower, water will build up and at a point the volume builds and breaks away, producing a drop based on density.

I don't remember the web sites, but more than one agreed that an average of around 25 drops would equal 1ml.

Ron