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Q & A: Best material for floating

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Most recent answer: 12/06/2012
what materail would hold the most amont of weight in water. example if i were to stand on something on top of water what would be the best and smallist object to standto float with out sinking. would it be traped air.
- mike orlopp (age 21)
newark,ny USA
Hi Mike,

Archimedes' principle says that the upwards buoyant force on an object is equal to the weight of the water that it displaces. This has to balance the downward force of your weight when you stand on it, as well as the weight of the material you are using to stand on. You therefore want some material that is going to be strong enough not to collapse when you stand on it while it sinks into the water, and light enough not to weigh very much.

Air is very light and when trapped can provide very strong forces. A thin, inflatable object like a rubber raft is an ideal way to trap air for floatation. Styrofoam works well too because consists mostly of trapped air. It may not be very strong however (and the rubber raft may have strength or stability issues as well). Balsa wood is also mostly trapped air. It is also porous and so may become heavy if it sits in the water too long.

You can do better than trapped air -- helium! It is be so buoyant that even without the water below a balloon filled with it will float away, due to the fact that the buoyant force of the displaced air is greater than the graviational weight of the helium plus the balloon. Please don't stand on gigantic helium balloons that are about to float away, however!


(published on 10/22/2007)

Follow-Up #1: Best floating material

looking for best floating material?
- Anonymous
huntington beach california

  Generally, the less dense the material is, the stronger the buoyant force will be.  The strength of the buoyant force may not be the only thing you may be concerned with, however.

  A substance which has a very low density and which is not too hard to manufacture is hydrogen gas.  If you fill a balloon (or dirigible) with it, it will float in air.  Hydrogen has the undesirable property of being flammable, explosive even, and large collections of it make for large explosions, as evidenced by the Hindenberg accident.

  You can put helium in balloons and blimps and they will float just fine.  Helium leaks out of rubber very slowly.  Blimps aren't very practical forms of transportation, but they work fine as advertisements and things to float over sports arenas.

  Hot air is less dense than colder air, and you can fill hot-air balloons with this material and they will float too.  Air can be heated with a flame and it's cheaper to use this than to buy a large amount of helium for a short balloon trip.  Sometimes cost and simplicity of storage and distribution is the overriding factor, not just the buoyancy.

  Substances lighter than air are usually gases (I cannot think of any liquid or solid
that's lighter than air at the moment.  Possibly an aerogel with helium in it might work..)
But then you need some kind of container to hold the gas.

  Did you mean floating on water?  Or oil, perhaps?  Styrofoam works pretty well for floating on water.  It isn't very rigid, and it melts at a low temperature.  It also decomposes if you leave it out in the sun for a long time.  If you're making speedboats, I'd not recommend making them solely out of styrofoam.  They'd float great, but they'd fall apart too easily.

  You can make combinations of things that have some components heavier than water (or air) that will float if they have large volumes of less-dense material inside of them.  For example, a steel-hulled boat will float if it has enough air space inside.  Steel is good for structural strength and low cost.  Most large ships are made of steel, although fiberglass is often used for small pleasure craft and sailboats.  You can also use just about any kind of wood, for ease of assembly and low cost, but it gets waterlogged, rots and isn't as strong as steel.


(published on 10/22/2007)

Follow-Up #2: plastic vent

i am trying to design a vent for a tank that contains gas (co2) and water I wish to evacuate the gas that builds up above the water because it prevents the water from circulating The problem is the vent can not contain any metal parts It must be made of plastic or a non ferous material There are many vents available but they are all made of metal. I wish to build my own so I need a material that will float and last to close a port in a small container (approx one inch in diameter by one and one half inches long) Thank you for your help
- sal mignone (age 77)
bohemia new york usa
I think that polyethylene is a good bet. Even the high-density (HDPE) type is slightly less dense than water. It's resistant to most typical chemicals, so probably it'll hold up in your application. Depending on how soft you want the material to be, maybe the low-density type (LDPE) would work better.

Mike W.

(published on 12/06/2012)

Follow-up on this answer.