Why Do Steel Ships Float When We Know All Metal Sinks?

Short Answer:Water displacement. The more a ship displaces, the weight the ship can hold.

http://en.wikipedia.org/wiki/Displacement_hull

There is no such thing as displacement acting as a force, there is an integral of pressure exerted on submerged surface of a floating object according to Pascal theorem. Imagine ship floating in one meter thick slick of oil spilled on the top of the ocean what would be the displacement then or sphere attached to the bottom of the sea with water pumped out from under it, it also displaces water but does not float to the surface as there is no force that would push it up.

Yours, Karol Karolak P. Eng.

Great response Karol, now does the same principle apply to Helium Balloons with the envelope made from lead sheet? after all Archimedes Buoyancy Principle also applies to gases, i.e. Air and with air's density about 1.29 kilos per cubic meter?

"Can I hear the strains of Jimmi Page on the guitar and John Bonham on drums?"

If you want to play with helium balloons (and not with sinking ships) try putting a few helium balloons in the back seat of your car, with all windows sealed and no AC fan going. Now drive. As you round corners quickly, the balloons will move to the inner side of the turn. Its because the heavier air has moved to the outer side of the turning vehicle, and the balloons are floating on the air.

That is a very interesting observation. Tie a rope to a bucket handle and you can swing the bucket with water round, and none spills. Artificial gravity, so a fast turning car would do the same with the air I guess. Folk here probably know I am currently obsessed with 'wacky' ways to get airborn. You have given me another 'idea' suppose one was to spin a large balloon? OK two balloons, because counter-rotation would make more sense, might it be possible to lose a bit of air to centrifugal forces? If it worked, perhaps make a 'saucer' shaped craft. We could hire Circus Midgets to dress up in shiney silver suits, put on green makeup, wear wierd contact lenses, and have antenae poking out of their heads. Then land outside a TV Station? ......April 1st maybe.

Huh?

im with u, i got bored in the middle of it

pure Water, at 4 C., has a density of 1.000 gm/cm3

Lithium Li has a density of 0.535 gm/cm3 and floats on water

Sodium has a density of 0.968 gm/cm3 and floats on water

Another way it floats is surface area. Take a peice of foil and fold it up then place it on water. Then take an unfolded peice of foil and presto floating foil. Has mainly to do with surface tension.

please extend on this

If you put a razor blade flat side down, on calm water it, too, will float. So, maybe ships are made of gently placed horizontal razor blades glued or welded together.

Sorry, I had to do that.

Ships float because they are mostly air, and with the exception of the large bubble which surrounds Atlantis, the air stays on top of the water.

Damn! I did it again.

Ships float because they carry so much oil, and oil not only floats, it repels water (as in 'oilskin') and this repulsion keeps the ships up.

Ok, okay, I'm sorry.

Ships don't float if they are made by General Electric's or General Dynamics' (one of those officer types) "Electric Boat Division". They make submarines. Maybe they have patents and other ships are not permitted to sink. That may be why captains go down with their ships, because they don't want to face the infringement lawsuits.

Interestingly enough, all-metal sinks float, too, if the plugs are in place.

I think it's like Peter Pan, and if we all believe, it works. The people on the Titanic just lost Faith. (She was third on the left.)

Let me go get my meds...

Thanks for the humor. Sometimes I wish I were clever that way. I would have to give you the prize for the most entertaining post I yet have read!

Seconded! Thanks for that, you don't need the meds, because 'laughter' is the best you will ever get.

Must be some of that lithium stuff mentioned above. great sarcasm.

milo

Play it safe, build your ship with lithium, it is less dense than water.

The oxidation of the hull would be spectacular!

It's all about the relative densities. The boat will float if the boat weighs less than what the weight of the same volume of water would be. That's also why if you fill a boat with water, it will sink :-)

The answer was found by Archimede about 2250 years ago. EUREKA !

For more details, ask directly him when you meet him in your future life.

The wood boat will sink for the same displacementin tons or kips per sq met= hight of sides or fb Harry

Why is it a wooden boat will only burn to the waterline? (And never burn a hole that water can pass through.)

Why does the waterline move as the boat burns?

The water is deathly afraid of it's arch nemisis the fire and in it's panic, retreats from the fire giving the impression that the burning ship is actualy becoming less massive and rising.

So the fire is aquaphobic (hydrophobic)?!

I hadn't heard that the waterline moved when a wooden boat burns, but thinking about it I would guess because the ship becomes lighter and less dense. That would cause the ship to sit higher in the water. I say lighter because the wood is converted to gas and carbon residue and I say less dense because the air in the ship is hotter and less dense, making the average density of the ship smaller.

Agree! And to answer jowens original question...Recall the fire triangle, fuel, heat and, air. Remove any one and you can't have a fire. As the wood burns thinner, the cooling effect of the water on the other side extinguishes the flame.

It reflects Archimides Principle. Essentially if you displace more water than your weight, you will float. If the amount of water displaced by an object weighs less than the object, then that object will sink.

Shielded metal can (hollow inside, of course) will also float on the water. Sealed empty glass bottle, also will. Full loaded untorn Titanic won't sink either. The key is that effective density of the body (whole body mass divided by water volume moved by) is lesser than water density itself.

Let the water replaces the air in the body, everything will happen as usual ... blup ... blup ... blup ... goo.oo.ood ..... bye, we take a journey to the bottom of the sea ... see you there .... blup ... blup ...blup!

I like the humour..... but suspect the original questioner is not an engineer......

Back to school methinks!!

A common push pin will "float" as well, and it weighs more than the water it displaces.

This can be demonstrated (my kids love it) by placing a small square of tissue paper on the surface of a glass of water. Carefully set a pin on top of the floating tissue paper. Gently push the tissue paper (which is by now quite soaked) down into the water. The pin will remain on the surface, floating in water.

SURFACE TENSION!

You can have even more fun with that by adding a drop (or maybe two) of Jet Dry to the water and telling your kids to give it a try. The pins will no longer float.

So that's true, as well as fun, but I'm pretty sure the effects of surface tension can be ignored when we are talking about even the smallest of ships.

Because of all the air, (which does'nt sink), inside.

K. I. S. S.

go to www.ask.com. type in "why do steel ships float when we know all metal sinks?"

out pops your answer

sorry, i'm mean.

Ok i guess we all forgot about the old high school experment of boiling water in a paper cup, also the fire triangle was replace with the tetrahedron with the new one added uninhibited reaction. but i still think all electical circuts work on smoke as if you let the smoke out of the wires the circut doesnt work no more

Now this is the best result of common sense....lol....

My what a motly crew we have grown to be..lol...

"Just let the smoke out"......lol......perfact.

Displacement......nice mind scan for the unknown......I guess our questionair was of the simplest of minds not understanding density, air, mass distribution,...molecular compounds.....qualities of compounds....fire, fuel, ignition,....extinguishings of elements with water,...such as air density or thus fuel saturation of common element.

Nice group of answers all, cudoes for all of you.

I do hope the question was answer so they were able to comprehend it all.

I thought we learned the answer to this question in elementary school?

Is this question real or for fun?

It is quite embarrassing that all the so called engineers out there never studied classical physics close enough to know that Archimedes principle is nothing but generalization of Pascal's principle. Integration of pressure of the liquid over submerged surface of an object generates vector of force.

For objects floating on a surface of water this vector force (resulting from integration) is directed upward and balances weight of the floating object -displaced volume multiplied by density (unit weight) of displaced fluid equals weight of floating object. Same principle works for Helium balloons as it does for suction cups with totally different results. Unfortunately these trivial things are not what engineers are taught these days.

Yours,

Karol Karolak P. Eng.

I believe that has been taken for granted.....

The questioner is asking a school physics question and as has been said is not an engineer.

John.

True, I wonder if the questionair has actually performed any type of displacement experiament with a variety of materials? Science is great when the unknown is actually discovered from performing the research with many samples and the information gathered from such test. Well anyway, is this blog finished or is there more to be added? Open for discussions.

It has been suggested the questioner is somewhat dumb and or ignorant and not an engineer. It is possible yet it is also possible that the question posed was ingenious for it developed some good stimulated conversations. I suggest since we are voluntarily contributing to the post rather than ignoring it we focus not on the whos but the whats and wherefores.

So rather than picking on the poster let us enjoy the return to simple physics; for some of us much reminiscence and revel in the discussion of one of the fundamentals of our universe. We can all use the refresher of fundamentals to help us stay grounded. Sometimes returning to fundamentals can inspire us in our more complicated pursuits.

What is the answer then displacement? And what is displacement besides the summing of the mass of the container: the steel and the air in the container and versing that against the forces of the water (pushing up or just resisting getting pushed out of the way by the container pushing or falling down)? What kind of easy experiments could be suggested to the poster to observe the process? Would someone like to show the math? Would someone like to write a small program showing the changes that would be effected by changing the thickness of the container and thereby changing the mass of available air for a container of a given footprint (displacement potential).

Speaking of footprint any one who has had an operation on an internal organ can tell you from experience that air can be infused into the musculature of the body; but how much air would need to be infused in the body for an average weight person with the displacement potential of a size 10 shoe to walk on water? What feat of will (subjective question) would it take to gulp in that much air and compress it into the body tissues?

Peace, Rollin.

Right on Rollin! Great posting, 'fundamentals' are key to understanding. We never lose when we reappraise them. I am still figuring out if a tube of high-strength woven cloth, say Kevlar, with a gas-tight low permeability internal membrane, then filled with Helium under moderate pressure, but still 'Air-Buoyant' could make a useful 'Strut' in a geodesic structure. a bit like building a boat out of balsa wood. You would make the structure lighter, the more struts you added.

Does anyone remember the link, I think it was a thread title that showed an aluminum foil boat floating in a heavier than air gas in an aquarium tank. Then the guy inhaled it and spoke in a very deep voice. I need to know what the gas was that was denser than air and apparently non-toxic. Thanks.

The noble gas Xenon, (54) 131.30, may have been the 'culprit'? for the deep voice. just a guess. Radon (86) would be out of the question, on health and safety grounds. For rather obvious reasons. It's radioactive!

From Wikipedia.

The speed of sound in xenon is slower than that in air (due to the slower average speed of the heavy xenon atoms compared to nitrogen and oxygen molecules), so xenon lowers the resonant frequencies of the vocal tract when inhaled. This produces a characteristic lowered voice pitch, opposite the high-pitched voice caused by inhalation of helium. Like helium, xenon does not satisfy the body's need for oxygen and is a simple asphyxiant; consequently, many universities no longer allow the voice stunt as a general chemistry demonstration. As xenon is expensive, the gas sulfur hexafluoride, which is similar to xenon in molecular weight (146 vs 131), is generally used in this stunt, although it too is an asphyxiant.

Thanks Alastair. It was sulfur hexafluoride. There is a thread "Inhaling Sulfur Hexafluoride" that links to a video that is fun to watch. Both the voice thing and they float an aluminum foil boat in an aquarium full of the stuff.

I love poopie

your dumb dumb i need an answer and u talk about poop...

Those who knows swimming will not drown , those who do not drowns or sinks and again comes up , we have taught steel two keep floating ...........you watch Titanic the movie and the doccumentary............as a..lesson.., than answer a simple question why do ice float even they are also "made up of" water

It's obvious. Density. If the boat's density is greater then water then it will sink. If not, it will float. If equal, it will submerge.

Density is measured by Mass divided Volume = Density. The reason why a crunched up foil ball won't float, but a boat-shaped one will is because of density.

Example: Let's say the Mass of the foil is 10 g. But the volume of the foil ball is 6ml, and the boat shaped one is 25ml.

10/6 (Ball)= 1.66666

10/25 (Boat Shape) = 0.4

Water's Density: 1.0

With this you see that the density is different. With metal, It's the same. (I used foil because you could check yourself). So metal cannonball can't float, USS Midway can.

my name is cody and im doing a progect on how metal boats float can you give me a quick run down.

Just read number 1 and 5.

im doing an essay, wich one should i read