Static Water Level in Well - Stone Drop Method

[KTurner]

Kturner On the speed of a rock falling - per your analogy after 3 seconds the rock would have traveled 32+64+96 = 192' so I cannot imagine how that is possible.

Not exactly. It continuously increases in speed (until it hits terminal velocity). So, at second 3, it's going 96 feet per second (ignoring drag), but it has just hit that speed. At second 2.9, it was going slower. This ignores air resistance/drag though, which slows things down some.

15 seconds sounds like a long time for something to be falling. A golf ball has a terminal velocity of 105 feet per second (~70mph). Even if it took 10 seconds to reach terminal velocity (dont know how long it would take), the golf ball would travel 525 feet (105 feet per second * 5 seconds) in the last five seconds.

Differently shaped rocks and different density rocks will have different terminal velocities. I.e., two dissimilar rocks dropped in the same well at the same time would reach the water at different times due to the differences in terminal velocities.

Keith

 

[Egon]

Differently shaped rocks and different density rocks will have different terminal velocities. I.e., two dissimilar rocks dropped in the same well at the same time would reach the water at different times due to the differences in terminal velocities./QUOTE]

Would the time difference measurement for that distance be within the capabilities of the ordinary person using his wristwatch?

Carl, my scholastic ability is also quite limited. Use the 9.8 ft/sec and forget about the sound time.

you could always work backwards from the distance measured and find the almost time it should take for the stone to fall that distance.

I'm best at stuff like that by putting a float on a fishing line and lowering that down the well.

Do you have a laser measurement device?

 

[Carl_NH]

Egon,

Agreed, keep it simple as possible. That's sort of my goal in this post to establish or determine somthing of a norm with this "stone drop" or "ice drop" as VIrotate appropriately suggested, as its simple, quick, yet effective to get a ballpark assessment +- 30' so to speak.

Indeed, the stone is clacking off the walls of the well on the way down is reducing velocity, but as you say working backwards, 56' in 3 seconds should be around 6 seconds to 110' and 12 seconds at 220' and so on.. and yes using a wrist watch. So my goal was/is some standard or "rule of thumb" with this. I did a search on this subject on TBN and looked at 30 or so different posts but couldn't find anything definitive.

i DO have laser measurement devices - one of those thermometers which is very good to see hot spots in piping or cold spots in walls. Now you have me thinking about getting another laser measurement device (like a golfer uses to get distance to the pin) same concept, just dont know how well it would work in a deep well which isn't always straight down and has pipe obstructions.

Thanks again.

Carl

 

[Carl_NH]

Keith.

Thanks for the golf ball analogy, typically when I play golf (26+ handicap) in 3-4 seconds after I hit it usually lands left or right it - not where I intended

Most of the time I am hitting the golf ball 150-200 yards (450-600') so 105 feet per second sounds about right.

Thats an accelerated speed, much like shooting a (stone, pellet etc) down a well not the same as dropping a rock and timing the free fall.

This has been interesting and hope this might help others trying to ascertain static well depth as it has me.

Carl

 

[Carl_NH]

Further to this, I plan to install a CSV or a Cycle Stop Valve and the low pressure cutout switch. After much reading today the CSV keeps the pump running during the cycle diverting the flow to the source as required while keeping the pressure under the setpoint.

This keeps the pump running and reduces the cycles on the motor which is what kills sub pumps from most of the time. @ $150 not cheap, but the longer life it should yield from the Sub motor should pay off plus lower electric costs due to the non cycling surge at startup.

Any suggestions on which CSV to get?

 

[TheGoose]

Carl,

I have seen ads for sonic water level testers, but they are about $1,000. I use a regular tape/weight, but around here our water levels are usually about 30-80 ft. We have 4" wells here so it's not quite possible to drop anything into the well without it getting wedged between the pump/casing.

I believe the acceleration is 32.2 ft/sec/sec as stated above. The math required to figure out how far left my mind years ago. Distance/velocity/acceleration.....all runs together in my head LOL. If you figure it out (seconds = x distance) let me know. Next time I measure one I'll drop in some chlorine tablets and see how long it takes to hear the spalsh and then correlate that to the measured water level.

 

[Carl_NH]

TheGoose,

Well I did figure it out with a tape measure 56' to water (after letting it sit most of the day) then did the stone drop. it was 3 seconds with my wristwatch, of course it might have been 2.7 or 3.1 seconds.. so 20'/second.

The stone was clacking on the well casing but I think for my purposes this is good enough. I will use 20' / sec as the average looking forward..

The other good one was to use ice instead of stones VIrotate suggested - lots of good ideas came from this..

Thanks

Carl

 

[nikdfish]

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deleted when I decided not to trust my rusty brain ....
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Nick

 

[Egon]

http://upload.wikimedia.org/math/6/e/5/6e551b7718cf4ab08290ff74ddc45ded.png
:thumbsup:

 

[wrooster]

TheGoose,
The stone was clacking on the well casing but I think for my purposes this is good enough. I will use 20' / sec as the average looking forward.
Carl

Carl,
A number of folks in this thread have already opined, but I don't think you are hearing it. So again: a pebble dropped into a well does not fall 20 feet per second. This is not a valid rule of thumb, and in is not of any use for the general case. You may have back-calculated that value from one experiment you did at a given water depth, but that does not make it a valid formula for all depths. Here's why -- from the moment you let go of the pebble, it is accelerating -- that is, falling faster with every passing moment.

The theory you need to know is explained here:
Gravitational acceleration - Wikipedia, the free encyclopedia

The practice that you need to know is explained here:
Equations for a falling body - Wikipedia, the free encyclopedia

Pay attention to the graphic of the basketball on the right side of the second link above. This is key to understanding the continued acceleration of a falling body.

You can use online calculators, such as the following, to easily convert between time and distance of a falling body. The first example calculator on the page can be used to convert time to distance.
Gravity Calculations - Falling Body Equations at gravitycalc.com

For example, using the calculator above ... if the stone dropped at the wellhead takes 3 seconds to hit the water below, the distance to the water is about 44 meters, or about 143 feet.

wrooster