If you jumped in, you would likely sink, due to the energy you have from your fall. However, if you carefully spread your weight out on the jelly, by lying down, the jelly would (probably) support your weight. Don't take my word for it.

Jelly may be more dense than water, but a swimming pool filled with jelly would not be dense enough for you and your mates to stand on, you would quickly sink to the bottom. Though not necessarily to your demise, whilst you will produce more drag trying to swim in the jelly you will also generate more force with your strokes, thus enabling you to swim reasonably well.

But if you do ever want to walk on the surface of a swimming pool then I would suggest custard as your medium of choice. Mixing custard powder and water in the right quantities creates a non-newtonian fluid which behaves like a solid when a sudden force is applied, enabling you and your mates to run on the surface of the custard filled swimming pool, this being the subject of many an internet video.

You shouldn't concern yourself with such trifles.

I doubt you would drown as long as you used basic swimming skills to float on your back and slowly swim to the edge of the pool, but you would certainly be in a jam!

The active ingredient in jelly dessert or jello is gelatin, a protein-based gelling product made from collagen.

Gelatin comes in different grades, or Bloom numbers, as measured by the force required to push a plunger into a solution of the stuff to a predetermined depth: the more rigid the sample, the higher the Bloom number. Jelly babies - a popular British sweet shaped like a miniature baby - have a high Bloom number, so there is little danger of drowning in a pool of the mixture used to make them.

The density of jelly is typically 10 per cent higher than water, so a swimmer would float higher in a pool full of jelly than in water. Jelly is also more viscous than water, meaning that someone diving into jelly might have difficulty surfacing. However, two researchers from the University of Minnesota, Minneapolis, won the 2005 Ig Nobel prize for chemistry for showing that people could swim just as quickly in water spiked with guar gum, an edible thickening agent, as in ordinary water. The spiked liquid has double the viscosity of water, yet the increased drag is cancelled out by the increase in thrust that swimmers can generate in it.

While we're on the subject of desserts, custard is interesting as it becomes much more viscous under pressure. It is possible to walk across a pool full of the stuff, as demonstrated on the UK TV series Braniac (for a clip of the feat, see YouTube).

Mike Follows, Willenhall, West Midlands, UK