The Splosh UK Forum

Did anyone else catch this piece in the current edition of New Scientist?

This week's question
SPLODGE...
I was having a discussion with my mates about what would happen if you filled a swimming pool with jelly and jumped in. Some of the group believe that you would sit happily on the surface. Others, myself included, reckon you would sink, and risk drowning as the jelly collapsed around you. We wouldn't want anyone to be harmed, so we don't recommend experimenting to find out. But do any New Scientist readers have a theoretical answer to the question?
Ross
Bristol

Perhaps some member here may already have the answer?

I would think it gets down to the specific gravity of the jelly and how big an arse one has!

Your answers and reasons here folks – but next weeks edition of New Scientist should have the boffins theories.

I like New Scientist and the pleb version Focus for exactly this sort of question. It is also brilliant at discounting urban myths...

I'm sure I've seen this on a kid's TV science programme but I can't remember the correct word, it's not viscosity but is something like that. There are certain substances, jelly might well be one of them, which will easily support the weight of a man as he runs across the surface but once the surface tension is breached it behaves as a liquid.

Now I'm going to walk on water, allegedly it's been done before

Richard wrote:I'm sure I've seen this on a kid's TV science programme but I can't remember the correct word, it's not viscosity but is something like that. There are certain substances, jelly might well be one of them, which will easily support the weight of a man as he runs across the surface but once the surface tension is breached it behaves as a liquid.

Now I'm going to walk on water, allegedly it's been done before

A non-newtonian fluid, I believe. Everyone's favourite, custard, is one! When impacted it behaves as a solid, but when treated more gently it acts as a liquid. Brainiac did it in an outdoor swimming pool in series 1, then brought it back later as a weekly feature. Don't think jelly behaves the same though. Pretty sure the weight of most humans would break the surface tension and they would sink.

It all depends on the amount of gelatin in the jelly. If there's a low proportion of gelatin the jelly will be watery and thin so you'd effectively start to sink. If there's a high proportion of gelatin the jelly is thicker and you MAY be supported by it, but you'd stand more chance of being supported if you were to lay down on it rather than stand on it due to the greater surface are you'd cover resulting in a reduced amount of pressure from mass.

Those of you who've seen vodka jelly will know it's more likely to be runny as people put too much vodka into it in proportion to the amount of gelatin.

It's quite likely that the temperature would also be a factor as the warmer the jelly gets the lower its density and the more likely you'd be to sink.

So the best way to try this would would be with a tall, waif-like supermodel in a very chilly pool and some volunteers to carefully place her on the jelly.

With regards to the custard example, I know the gadget show did something on it earlier in the year with Gail Porter. I don't think jelly is a non-newtonian fluid in the same way as it is solid, in normal conditions (and with enough gelatin).

I think it might work if you mixed the jelly with cornflour [cornstarch] as the thickening agent along with gelatin. This would also make the jelly cloudy and more viscous, perhaps, this would be better for sploshing.
Arrowroot would thicken the jelly without the cloudiness but I 'm not sure about the qualities of the resultant mass.
What fun finding out.
With suitably dressed laboratory assistants of course. Maybe Abby from NCIS could be in attendance.

Great thread! I think someone would probably break the surface of the jelly and sink.

On another matter, Jon makes perfectly set vodka jellies, despite being teetotal. Perfect boyfriend and scientist

This type of thing is why I love this forum.
Don't know the answer but I sure wish I could have a go at finding it out

Thank you splosherrob! "Non-newtonian fluid" is exactly what I was groping for through the effects of red wine

eden wrote:Great thread! I think someone would probably break the surface of the jelly and sink.

On another matter, Jon makes perfectly set vodka jellies, despite being teetotal. Perfect boyfriend and scientist

Goodman Jon...... Bring somewith to the next meet, I'm sure we'd take the time to sample.........


regards

Andy

I'm not very keen on jelly so can I just have the vodka please

Mouse eats vodka jelly for breakfast! And being very small could probably walk on it. Personally I like jelly and I like vodka but not the combination, smacks of lilly gilding!

andy250 wrote:

eden wrote:Great thread! I think someone would probably break the surface of the jelly and sink.

On another matter, Jon makes perfectly set vodka jellies, despite being teetotal. Perfect boyfriend and scientist

Goodman Jon...... Bring somewith to the next meet, I'm sure we'd take the time to sample.........


regards

Andy

I put it down to being teetotal, I made it with the intention of it making jelly rather than being super strong.

And I think you'd sink in set jelly since it is a solid, although you can probably make it to varying toughness, and maybe with enough gelatin you'd make something a bit more like rubber than what you'd usually think of as jelly.

Incidenally, I think you'd probably float in unset jelly mix, while it's still liqud, since it'd probably have properties like salt water due to a slightly higher density...

And semi-unset jelly would feel a lot nicer too!

Thank you folks for passing on your thoughts,
As soon as the next New Scientist hits the stands and give you all the boffins answers.