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How strong would a vacuum cleaner need to be to pick up coins from a 26ft deep wishing well?

asked in physics, vacuum cleaner

beeper_spryte answers:

a normal vacuum cleaner with a 26' hose would do.

Supplement from 09/18/2008 07:00pm:

or strong enough to support the weight of a 6 year old - i hear you can train them for tasks like these :p

(sorry mate, i'm in a devilish mood the night) >:)

Supplement from 09/18/2008 07:12pm:

good point made by kent - are we talking about a 40-year old traditional hoover? a shiny vax? the latest dyson?

i still vote for sending the small child down on the end of the hose to hand-sort them...

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KentPDG answers:

Assuming a typical 1=1/2" hose, each foot of hose would contain about one pound of water. Hence, while sucking, the 26 feet of hose would have to lift about 26 pounds (actually, 25.35) pounds of water.

That might be quite a load for a typical household vacuum cleaner. Houshold vaccums are designed to create high velocities of air, but not to do much lifting. The lifting is done, to a large degree, by the rotating brushes in the vacuum cleaner. The fast-moving air stream then adds velocity to the particles that have been brushed up (although, of course, some are just sucked up directly).

Shop vacuums, known as "wet-or-dry" vacuums, are designed to ingest water as well as air. However, they would not serve to pump out, say, a foot of water in a flooded basement if the hose were extended down from the first floor. The motor would burn out pretty quickly.

The power you would require in a pump would depend on how deep the water is in the well. If the water level were at the surface of the well, with water 26 feet deep, a shop vacuum would probably do the job. If the water level was, say, 26 feet down, then you would need a more powerful pump.

Typical well pumps are from one to three hp.; but they usually supply only about a one inch hose. For a hose large enough to pick up coins of various denominations, you would need more power. But because you would be pumping a column only 26 feet high (not 100 or 200 feet), the power requirement would be lower.

So I would say a two hp. pump would probably do the job. So long as you could get over the ethical hurdle of stealing everyone's dreams represented by all those coins at the bottom of the well.

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wumpus answers:

The more recent "copper" coins are attracted to magnets.

If you were to lower a magnet on a string, you wouldn't get the older coins but you'd still get a good haul.

Supplement from 09/18/2008 09:29pm:

Thinking about it again; the depth of the well doesn't matter at all.

Just lower the vacuum cleaner down the well on a long rope, and haul it back up again once finished.
(Don't use the power cord for lowering/raising it!)

Of course, you'll need to attach a long rod to the nozzle, so you can control it at a distance...

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Sr2k5 answers:

Quite Strong?

Try a Dyson - see if it works :)

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Messerwisser answers:

If there is water in the well most vacuum cleaner would have an electric shortcut.
And those who can handle water have such a limited suction that they are not capable to lift water that high.
The theoretical lifting height is 10 meters, but in practice it is less than 8 meters because of air in the water.
Throw a coin in the well and make a which that the other coins will get up!

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kev_from_edinburgh answers:

if you take water out the equation, and just think air, then the suction of the vacuum would have to match and surpass the air pressure around the coin while experiencing terminal velocity.
anything less than that and the coin will fall instead of raise.

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