OT: Sink or Float?

[~tb]

So, if the monitor's tube weighs X and the surface area is X*the square of the surface area, and that resultant equals anything more than the surface tension and mass of the water, it will sink. If the surface area is greater than the mass*the surface tension and mass of the water, it will float.

Bob,

I disagree with your surface area theory. Maybe it is how it is done in the kayak industry, but this is purely a displacement problem. Take a cube and a sphere of equal mass and volume (V= 1m^3 and M=2kg). The cube has more surface area comming in at 6m^2 in comparison to the sphere at 4.835976. When submerged in the water they displace the same amount.

now lets make them bouyant at say .95 kg for the same 1 m^3 of volume. they will both float. They will both float with the same volume suspended ABOVE water.

Disagree?!?!? Show me your work that you can give me a plausable situation where the cube, with its increased surface area floats while the sphere with its decreased surface area sinks.

~tb

[Jack M]

Let's say you have an object weighting 20lbs. If that object is a bar of steel, it'll zip to the bottom. If that object is made of the same steel, but is say, in the shape of a boat hull - meaning it has been thinned and shaped to 'displace' - it'll float. (As long as you don't fill the inside with water which adds weight to the boat.)

well sure, but you didn't say anything about displacement at first.

Really? Are you sure? Show your work. :)

No, Todd has the right answer of course. I wasn't considering the density of the rock.

But what about the water that evaporates when the rock causes a splash? ;)

[Jack M]

Now get a long extension cord and plug that sucker in!!!

[Guest Randy S.]

Now get a long extension cord and plug that sucker in!!!

Exactly what I was thinking.

Thanks for the movie. Glad to know I was right.

Postcount +1

[Rob-CanCarve]

Being absolutely useless with math - the only thing I know for sure is that the monitor is not going work after this experiement.

Hope everyone is having a great summer.

All the best,

Rob

[Guest Randy S.]

Being absolutely useless with math - the only thing I know for sure is that the monitor is not going work after this experiement.

Hope everyone is having a great summer.

All the best,

Rob

Something tells me it didn't work before the experiment.

[C5 Golfer]

Now shoot it with one of the guns in the other thread or better yet a Barret 50BMG and take a movie of it?

Be sure to use a high speed Kodak so we can slow it down and have a beer while it slowly make a big friggen explosion.

[Derf]

Being absolutely useless with math - the only thing I know for sure is that the monitor is not going work after this experiement.

Hope everyone is having a great summer.

All the best,

Rob

Itts funny sometimes. Once I picked up a monitor that was left outside in the rain. I let it dry for a couple of days, plugged it in and it worked (but it did not work well, that's why it was on the side of the road). At least I disposed of it properly, unlike its previous owner.

[Guest johann]

Please tell me ya'll didn't leave the monitor in the water.

Hate to be a tree hugging hippie fag, but the surfrider in me is appalled!

[~tb]

Please tell me ya'll didn't leave the monitor in the water.

Hate to be a tree hugging hippie fag, but the surfrider in me is appalled!

go re-read post number 23

[Jack M]

Bob, I think your equation is just a roundabout way of saying if something is less dense than water then it will float, yes?

For instance, an empty glass beer bottle will float if you screw the cap back on. This is because when calculating the density of the bottle, the mass of the bottle is just the mass of the glass plus the mass of the air inside (negligible), but the volume includes the 12oz air pocket. If you take the cap off and allow the bottle to fill with water, then the mass of the bottle is just the glass, and the volume is just the glass also, and glass is more dense than water, so...

Of course you knew that already, but I don't think it needs to be any more complex than that...?

[Guest johann]

ma bad, thats what i get for not reading the whole thread heh heh

[~tb]

Alright,

so please dont post to the following thread, as these people wont get the answer till MONDAY. . . but worth the read.

One of my friends here at work posted the same question to a oline forum group that he is active in called headfi. People that spend way to much money on headphone instead of the more important snowboards. Anyhow . . . worth the read. I guess this proves that snowboarders are smarter than headphone geeks.

http://www6.head-fi.org/forums/showthread.php?t=131920

[Jack M]

sweet. Have your friend tell Yngwie Malmsteen that he sucks at guitar.

:D

One of the posters has a point - some monitors like Sony Trinitron are lined with lead. I bet one of those might sink.

[Mike Tokar]

I'm intrigued by this thread even more than the OT 'men are from Mars, Aisling is from Venus' one.

As far as my prediction regarding 'Will it float?", I say it will float only because I'm an optimist. You can't keep an old monitor down!

BTW, on Letterman, don't they just drop the object into the tank and let it work itself out from there? If I'm wrong and it just stays down, I'd request the test be conducted like on the show. It's kind of mean to dunk the thing first and hold it underwater.

So, when will you post the actual answer for those of us that have quicktime issues?

MT

[~tb]

Mike,

It does indeed float. Even if you try to make it sink (within reason), it pops back up to the surface.

-Todd

[Jack M]

Not really.

The steel an air craft carrier is made of certainly is not 'less dense' than sea water.

The steel itself is more dense than water, yes. But a boat hull made of steel is less dense than water. The mass of the boat hull is the mass of the steel, but the volume of the boat hull includes the cavity in the hold. I thought that's all that mattered.

I can't imagine floatation depends on surface tension by a very significant amount. If it did, then you could sink a battleship by dumping soap all around it (breaks surface tension).

But I think I see what you mean about surface area. I'm imagining myself floating on my back in the pool, all spread out, and then tucking into a cannonball shape. I'm sure more of my body would be below the water in a cannonball tuck.

[kjl]

The steel an air craft carrier is made of certainly is not 'less dense' than sea water.

Yes, but the steel + the enclosed airspace under the water line is definitely less dense than sea water.

To address Todd’s ‘Sphere/Cube’ example, that only addresses displacement and buoyancy. It does not address pressure and surface tension.

For instance. The vertical sides of the cube have no pressure on the water surface. (Vertically or gravitationally acted upon) If the same density material object were flattened to expose more horizontal surface area to the water, more mass would be above the water line than that of the cube.

Ultra nerd alert:

The upward (vertical) force of water on a small section of submerged hull works out to be the overall pressure of the water * the area of the horizontal footprint of the submerged hull. By "horizontal footprint" I just mean the total area of the hull piece if you were to take a picture from directly below. I just worked it out on some paper here, but if you want I can scrawl it out with mspaint or something and throw up my diagrams.

e.g. a piece of hull with a 1 sq in horizontal footprint that is completely flat pushing down against water at 1PSI will experience a vertical force of 1pound. A piece of hull with a 1 sq in horizontal footprint that is tilted up 60 degrees will experience only .5 of vertical PSI ( cos(60)*1PSI ), but the actual surface area of the hull is 2 sq in (1 sq in / cos(60) ). 2 sq in * .5 PSI = 1 pound of vertical force.

Since the vertical force is constant per square footage of horizontal footprint, the only thing that changes the total vertical force is the actual PSI of the water, which increases linearly with depth. e.g. a 1 sq in of hull at a depth of 5 inches experiences 5 times as much pressure as a 1 sq in of hull at a depth of 1 inch.

i.e. the vertical force acting on a very small piece of hull = horizontal square footage * depth * some constant.

If you take the entire boat hull and add up the vertical force for each little segment of hull (each of equal horizontal footprint), you are essentially integrating the depth over the entire hull. The integral of the depth of the hull == the volume of the hull under water.

Ergo the force acting upwards = some constant * volume.

Force acting downwards = mass of boat * gravity.

Buoyancy force = some constant * volume - mass * gravity.

So surface area doesn't matter, although if you have a very flat, wide boat and a tall, narrow boat of equal weights, the tall, narrow boat will sit lower in the water, but only because its horizontal footprint is smaller - When both boats are at equilibrium, the submerged volume of both boats will be equal.

[~tb]

ill entertain this one. . . but how much of an impact will surface area really have? Would it make a rats ass of a difference on something say. . . the size of a computer monitor? I would hazard a guess at "no" and that the bouyancy is more of a contributing factor than any impact of surface tension. How large of a test piece would I have to fabricate to see first hand that surface area plays more of contributing factor than the fact that I farted right before putting the monitor into the water.

[mirror70]

I'm biting my tongue because I have unpopular things to say in very unfriendly ways

But basically, for anecdotal proof that Bob is "in over his head," think of the surface area the monitor has once you submerge it. It's probably a number similar to Bob's 18lb kayak. More would be to try floating while fully clothed and see what effect that has. As Jack said, see how much of your body stay above water when laying on your back compared to crunched up - your surface area doesn't change.

On a side note, Erik, if you're reading this, can you email me?

[dantheman0177]

If you are in a boat and are holding a rock, say about 10 lbs and about 1 foot in diameter, and you toss the rock into the water. Will the water level rise? Or fall?

I'm no engineer, but I think it has to do with the displacement of the boat hull and the total mass of the boat. After that I start to get a bit lost. I have been thinking about this in relation to using my two racing kayaks, both of which have the same weight but different hulls and displace different volumes of water, but honestly I can't figure it out.

My gut feeling is that the water level will rise regardless, unless the boat has a hull design which, at the reduction of weight caused by the release of the rock, reduces the volume of water displaced by the hull exactly to the amount displaced by the rock, therefore making the water level drop for the period while the rock is in the air, and then rise again when it is enveloped by the water (playing semantics a little here) and ultimately not changing.

What grade do I get for that answer, professor?

[k_t]

ill entertain this one. . . but how much of an impact will surface area really have? Would it make a rats ass of a difference on something say. . . the size of a computer monitor? I would hazard a guess at "no" and that the bouyancy is more of a contributing factor than any impact of surface tension. How large of a test piece would I have to fabricate to see first hand that surface area plays more of contributing factor than the fact that I farted right before putting the monitor into the water.

I kind of liked this read when it was on the lighter side, like when guns were involved in disposing the monitor or just plugging it in after it were afloat. On that note, Todd, are you saying that the results were not accurate because you may have added buoyancy by farting into the vent holes?