# a pint rests on this

B

#### breezer

sorry you only get a virtual pint, but i get a real one (hoepfully)

The facts

a pipe is laid on a horizontal stand with a hose connected to it

at the same time two holes are verticaly into said pipe

one hole is 1/8th of an inch

the other hole is 1/4 of an inch

under each hole is a bucket marked in 1/2 litres

hose will not be turned off for this "test"

The questions

from which hole will the water go highest (i say the 1/4 inch)

which will fill the bucket to one litre first (i say the 1/2 inch one)

two holes are verticaly into said pipe
eh?

And they measure 1/8, 1/4, and 1/2.

But the answers are yes and yes.

I say the 1/8" hole will produce the highest fountain as the velocity through this is higher than the 1/4" one.
If it's pointing towards the bucket the 1/4" hole will fill it quickest.

no matter what size hole, customer wants u to bloody fix it , not debate it and tell them what size bucket they need.lol

NON IF YA HOSE AINT TURNED ON 4 THE TEST,

bab said:
NON IF YA HOSE AINT TURNED ON 4 THE TEST,

but he said it wont be turned off?

highest: 1/8

bucket fill fastest: 1/4

OOPs i dont need any more beers 2 night.words r jumpin around.

so which is right?

neither.cuz the pipe is open @ the opposite end to the hose

If the hose itself has no resistance, the pressures at the holes (assuming they're all pointing upwards!) will be the same, and equal to the head of the water supply. You have to assume there re no pressure drops due to flow through the pipe. If the supply were from a tank of water, all the jets would , without resistances, go up to the level of water in the tank.

But there are resistances. The surface tension in the water IS signficant, and would have more effect on the smaller diameter jet, because there's a higher surface/volume ratio. It isn't too difficult to calculate if you know the constants for water, the temperature, etc. Anyway the thinner jet doesn't go as high becasue of the surface tension, which basically tries to hold the water against the metal at the edge of the hole.

There's no reason why the speed of the water should be greater from the smaller hole.

Lots more water comes out of the bigger hole, obviously. A) it's bigger, B) less resistance.

Ignoring the resistance of each hole, if the pressure at the two holes is the same, then the flow rate from the holes will be the same.

The Venturi principle dictates that, in order to achieve the same flow rate, the velocity of water from the smaller hole will be greater, hence its jet will be higher. This assumes that the trajectory of the jets is the same, e.g. nearly vertical (a vertical jet would introduce too many complexities since there would be falling water landing back on the hole).

The smaller hole is likely to offer more resistance to the flow, but whether or not the extra resistance of the smaller hole is enough to reduce the jet to be the same as, or less then, the larger hole, is dependent on the head of water and the resistance of the hose and the pipe, so the first question cannot be answered without more information.

Similarly, ignoring the resistances, since the flow rate is the same from each hole, the bucket fill time will be the same.

However, taking into account resistances, it's likely that the net flow rate from the smaller hole will be less than from the larger hole, so it will fill the bucket more slowly.

There are other considerations; for example, if the head of water was low enough, then it's possible for the hole nearer the supply to starve the further one, resulting in negligable flow from the further one. So the second question can't be answered without more information.

A poorly constructed question if ever there was one - I wouldn't bet a pint on the answer.

BTW, I don't understand the purpose of the bucket being graduated in 1/2 litres.

Softus said:
if the pressure at the two holes is the same, then the flow rate from the holes will be the same.

thats just jobbies Softus

asc said:
Softus said:
if the pressure at the two holes is the same, then the flow rate from the holes will be the same.
thats just jobbies Softus
Could you explain that comment, preferably in an intelligent manner, and bearing in mind the whole sentence from my posting, not just the fragment that you've quoted?

Softus said:
Ignoring the resistance of each hole, if the pressure at the two holes is the same, then the flow rate from the holes will be the same.

Edit:

Cancel that last request - I've just had a look at some of your other postings, and there's very little chance of you posting anything remotely intelligent on this topic.

Ignoring the resistance of each hole, if the pressure at the two holes is the same, then the flow rate from the holes will be the same.
NO, you don't mean that! The SPEED of the water would be the same, the flow rate, in volume per unit time, would be proportional to cross sectional area of the hole.

The Venturi principle dictates that, in order to achieve the same flow rate, the velocity of water from the smaller hole will be greater,
No, it doesn't say that, and it doesn't apply here. The bit you're half-quoting applies in constrictions in closed pipes. This isn't a closed pipe. The venturi stuff relating to holes in pipes says how the pressure in the side of the constriction is less... - different thing altogether.

Look chaps, when I was at the Vogun Dam in Vakhsh, Tajikistan, I thought about this. It's over 300metres high. If there were holes in the dam wall, pointing upwards, at whatever angle, the water would come out, and up, right up to the level of the water behind the dam. It wouldn't matter within reason how big the holes were (say a metre or so across), because their resistance would be insignificant.
If the hole were angled up at 45º the water would come out at 250mph and land 1200 metres away, but I digress.

If you don't believe me about the water going back up to the same height, imagine it with a tube to guide it. If the water's in a jet, it's the same shape as it would be without the tube - the tube is "doing" nothing if you again ignore surface tension. If the top of the tube were just below the water level in the dam, water would come out of the tube.

OK??

ChrisR said:
Ignoring the resistance of each hole, if the pressure at the two holes is the same, then the flow rate from the holes will be the same.
NO, you don't mean that!
Chris, I did mean it, but I understand your comments and I'll have another think.

ChrisR said:
The SPEED of the water would be the same, the flow rate, in volume per unit time, would be proportional to cross sectional area of the hole.
Hm. I don't see why. Yet...

Also, I don't (yet) agree that the dam water would follow the same path as it would if it were in a tube, but I don't have a scientific reason for disagreeing, so, again, I'll cogitate.

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