Say I had a very large watering can with a small spout. Like this one:

Then say I was on the roof of a very high building pouring water out of the can in one steady, slow stream so that I could watch it hit the ground many metres below.

Questions: 1. Would the stream break up before hitting the ground? 2. Would the answer to question 1 be different if the stream was long enough to hit the ground before the watering can was empty?

1. Yes
2. No

dont ask me to show my workings.

1. Yes, if the building is high enough.

2. No. Look at a high waterfall, which has basically an infinitely large watering can. Stream still breaks up. the ground can’t affect what happens to the stream higher up.

What if you pour the water in a vacuum?

I should have added a third question. If it does break up, why?

I am basically wondering why matter that is bonded together to greater or lesser degrees, will more often than not fragment in travel even if the release rate is the the same across it.

In other words, if I catapulted a lump of jelly at a wall I assume it would splatter in many different drops instead of hitting as an in-tact blob and a single splat.

EDIT: The waterfall is a good analogy. Thanks. Although I would argue that because it is spread out to begin with, and there are unseen obstacles in the water, it doesn’t work as precisely as I want.

The forces exerted by turbulence become greater than surface tension?

hahahahaha im laughing at myself for saying this, but I think they did this on Nina and the neorons. It was certainly on something on cbeebies.

In other words, if I catapulted a lump of jelly at a wall I assume it would splatter in many different drops instead of hitting as an in-tact blob and a single splat.

Jelly – Yes.
Custard – No…. Non-Newtonian Fluid, innit! 😀

Turning on my model waterfall (kitchen tap), there would appear to be a point in terms of flow and volume where:
It as a trickle, breaks up
It flows nicely as a single smooth column to the sink base
As a torrent, it breaks up.

Flow rate, volume and height are the variables, though I guess temperature if its close to 0 degrees or lower may affect this.

Well, you’ve got turbulence in the stream, but a bigger effect is air resistance – it’ll shear droplets off the sides of the stream, and eventually make it break up.

In a vacuum you wouldn’t have that, but the water would be boiling away so end result would be the same.

A stream of mercury in a vacuum might be as close as you can get to staying together – though at some point it’d freeze and be a solid rod of mercury. It’d freeze from the outside, so not sure how that’d change things.

What does the build of the watering can have to do with the behaviour of a stream of water moving through space under gravity, towards an obstruction?

@Woppit: I just wanted to distinguish my model from one of these:

For obvious reasons. Although I love yellow.

Custard – No…. Non-Newtonian Fluid, innit

Did you watch 6 Degrees of Separation (or something like that it was called ) last night.

I’m now very tempted to hit the next bowl of custard I’m served with a mallet 😆

Edit … a custard watering can !! …. Win win

For obvious reasons. Although I love yellow.

SWYDT. Very good. 😉 😆

perchypanther – Member
I
Jelly – Yes.
Custard – No…. Non-Newtonian Fluid, innit!

Only if the starch ISN’T cooked – cook it so its custard (ie edible) and its not a non-newtonian liquid anymore. It’s not custard until you cook it 😛

Did you watch 6 Degrees of Separation (or something like that it was called ) last night.

I did, yes. Thought there should have been more intelligent comedians and less unfunny scientists but quite good for a first effort.

The definitive work on non-newtonian fluids in general and custard in particular
was the successful attempt by, ex Big Brother dweeb, Jon Tickle to walk across a swimming pool full of custard on the excellent Brainiac: Science Abuse series.
The work firewall prevents me uploading a youtube link however.

The stream of water is accelerating as it falls and therefore is stretching.

Think of 2 particles that came out 1/100th of a second apart. As they leave the spout they will be close together. A few seconds later they will both have accelerated at the same rate but the distance between them will be greater. At some point the surface tension will not be strong enough to hold them together so the stream breaks.

(Look at a row of F1 cars round a corner, when they’e slow they bunch up when they’re at full speed there’s a space between them but they’re still separated by the same time)

Drag from the walls of the spout will cause turbulence in the water causing the jet to break up in a high flow situation.

A combination of air resistance on the edges of the stream and the acceleration and therefore stretching of the stream as it falls will also overcome the surface tension in lower flow situations.

Therefore for any feasible watering can and high wall, you’ll always get drops at the bottom.

you also need to consider the differences in flow of a ‘tension’ surface (i.e. water interfacial tension) and internal friction. The water in the centre of the column will move under less friction than that at the outer edge. complicate this further with the tension developing at the end of the flow before it hits the ground and you have a build up of internal pressure which can only equilibriate by expanding the column, maybe leading to break up. In a vacuum, with no air to resist against, don’t know, guess it’ll all depend on height and velocity.

I’m pretty sure there’s a very complicated way to explain this in physics terms, but I’m a geochemist, so will just go with the theory. 😉

Stokes equation no?

https://en.wikipedia.org/wiki/Stokes_flow

I’m pretty sure there’s a very complicated way to explain this in physics terms

The simple way is good enough.

You could reduce the turbulence within the fluid with a lamina flow nozzle in the watering can

ala:

say I was on the roof of a very high building pouring water out of the can in one steady, slow stream so that I could watch it hit the ground many metres below.

Questions: 1. Would the stream break up before hitting the ground? 2. Would the answer to question 1 be different if the stream was long enough to hit the ground before the watering can was empty?

OP why don’t you just try it and let us know how you get on?…..’s the Scientific Method, innit! Attempt to disprove your hypothesis by experimentation. Publish results for peer review.

Is there a conveyer belt involved?

The conditions for laminar flow are very precise. Because the water is being forced through the nozzle (by the weight of water above it), you’d get turbulent flow.

Crack open a tap slowly and you might see laminar flow – where the water moves at the same speed throughout its cross-section and looks like a solid rod of glass.

As soon as you increase the pressure slightly, you get turbulent flow and the water behaves far more erratically.

You think that’s confusing…what about this?


Not mine, but works a treat.

A laminar flow nozzle reduces the turbulence and increases the effective strength of the surface tension. But the stream will still break apart when the acceleration of gravity stretches it enough. In the picture above, the stream is pointed up so there is no break up before it hits the ground.

Alton Towers used to have a display of those by the entrance and the streams used to split into sausage shapes, which was quite entertaining.

A jet turning into drops is fairly complex, but has been understood for over a 100 years (see Lord Rayleigh). A vertically falling column of liquid will break into drops, depending on a number of factors.
It’s important in ink jet printing. (Not your HP desktop, the really high speed ones that print best before dates. Here the drop formation is controlled by added pressure waves, but Lord Rayleigh is still important).