Archive: 27 posts

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OK, come on, it's December twenty-third already and I still don't see a complete treatise on the physical properties of LBP water. This is LBPCentral! I think there's a lot of budding boat builders becoming bewildered and begging for a better base on buoyancy. And frankly forwarding frigates is finding me frustrated...fancy a force a bit like friction, yet feels fictitious. (That's my allowance for alliteration alas...or perhaps "at last!". ) Is there something already available? Does somebody want to take a crack at it? (RTM, I'm looking at you. :arg: ) If not I'll start adding to this thread as I get things sorted out.

2009-12-23 18:26:00 Author: LittleBigDave Posts: 324

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Ya, I caught your profile message. I'm not gonna have time to contribute properly until after xmas I'm afraid. For now, you get ramblings. First off, check out: https://lbpcentral.lbp-hub.com/index.php?t=t=8914&highlight=weight+measurements Take the weights in that table to be relative densities. Water has a density of around 15 - it's slightly off last time I checked, can't remember in what direction. This is so that wood floats and metal/stone sinks I guess. Note that this makes metal and stone only 1.3x the density of water, rather than the ~10x IRL. Also note that poly is < 0.1x density of water, hence why it floats so high. Glass is the same density as wood which is why it floats - this is not stupid, it's consistent. Other than that, water physics is basically the same as air physics. Gravity still applies as does resistance. However water resistance is many times greater than air resistance and gravity is opposed by upthrust (see above paragraph on densities). Air / Water resistance seems to be based upon volume of material, so solid paddle wheels work better that actual paddles The resistive forces being quite heavy mean that fast moving connectors moving light (low density=>weak) material on them will break it! Raising / lowering the water level does affect upthust - important to note. Nothing about water physics is particularly odd. It's just that for the most part we don't have to take much into consideration when working in air, water is just less forgiving.

2009-12-23 19:02:00 Author: rtm223 Posts: 6497

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One thing that I've come across is that if you use water sensors to change the water level, so that it keeps going up and down between the sensors, and one of the global water objects is set to change faster than the other, your sackperson will be pulled down or pushed up, depending on which G.W.O. is faster.

2009-12-23 22:06:00 Author: Hibbsi Posts: 203

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Here (http://www.lbpcentral.com/forums/showpost.php?p=350088&postcount=223) is a post on non-rocket propulsion that I (yay for self promotion!) couldn't be bothered to type out again. paddlewheels are inferior to...wheels.

2009-12-23 22:57:00 Author: Memodrix Posts: 879

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Here's a few things I know. -Metal and Stones are the only ones that don't have much buoyancy -If a material/object is on fire, it goes out once it is completely submerged in the water And that's about it

2009-12-24 01:00:00 Author: psman012 Posts: 106

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I have a level which explains all the material physics! Just search @plasmavore, I can't remember the name sorry

2009-12-24 12:26:00 Author: Plasmavore Posts: 1913

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Glass is the same density as wood which is why it floats - this is not stupid, it's consistent. It's unfortunate that they chose the density of glass this way when first designing the game. But changing it now would break loads of existing levels, so it's the only option.

2009-12-24 16:33:00 Author: Rogar Posts: 2284

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At least that allows us to use it for floating icebergs.

2009-12-24 16:38:00 Author: Syroc Posts: 3193

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At least that allows us to use it for floating icebergs. Hey, that's a good idea!

2009-12-24 18:32:00 Author: psman012 Posts: 106

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Just remembered the level name, it's "Water; Tips & Tricks" by plasmavore

2009-12-25 20:33:00 Author: Plasmavore Posts: 1913

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OK, my working understanding so far is that if an object had an overall density equal to that of water, then it ought to remain stationary if placed anywhere between the sea's surface and floor. (This assumes calm water = zero waviness setting.) As RTM223 helpfully pointed out, water seems to have a density of about 15 (= 15 times the density of cardboard, cardboard being the lightest positive mass material in the game). So I'm thinking if I glued a block of wood (density = 10) to an equal-sized block of metal (density = 20), that I'd have an object with an average density overall of 15. If it floats up, then the density of water is more than exactly 15. And likewise if it sinks, then the density of water is less than 15. (I could then rewind and keep tweaking the ratio of wood to metal until my object remained still, and whatever average density makes that work is the exact density of water.) But here's where I go from possibly confused to definitely confused: If I build a 12.5x10x1 block of wood and glue it to a 10x10x1 block of metal, it sinks. Yet if I take that same construct, copy it, and shrink it down (shrinking as much as I can with small grid on - so it's small, but not microscopic), it instead very slowly floats up! This is with both sized objects starting at rest fully submerged. Does this mean there's an additional force pushing up or down that is dependent on volume only? Or maybe it has to do with the physics engine generating a resistance acceleration (resistance being volume based) greater than (but still opposite to) the buoyancy acceleration?

2010-01-02 22:17:00 Author: LittleBigDave Posts: 324

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Interesting find though, and it certainly deserves some thought. I'm a gonna get my speculating hat on.... But I'm drunk and I can't find it SO I'm gonna just speculate anyway... Make what you will of this If I remember correctly, MM told us that water forces consisted of upthrust and dampening forces. Weight is proportional to volume already, so I don't think this is an issue related to volume directly. I may need to go back and check the concept of gravitation within LBP for this one. Smaller objects fall slower in air and I have been attributing this solely to air resistance, but this could be wrong. Maybe the smaller objects actually have a lower value of g, so that gravitational force is reduced, but the upthrust force is proportional to volume. Or maybe it's the other way around, with an inverse somewhere.... I'm gonna give up trying to be clever around now, considering my current state, I think.

2010-01-03 00:08:00 Author: rtm223 Posts: 6497

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rtm223: I think many a great scientific leap had a bit of alcohol propelling it across the knowledge gap...so keep up the good work. I'll have to play around with these things above and below the water line. Regarding forces at work in water, besides the upthrust along the Y axis, there also seems to be seem kind of "wiggling" force along the X axis....or at least I find it impossible to maintain an unstable equilibrium. For example, make a long rectangle of wood, and try placing it so its long end is along the Y axis. In my experience it will always turn sideways regardless of careful starting conditions. And if I make a small thin construct of floaty glued to metal, it will actually keep wiggling slightly back and forth indefinitely, pivoting about its center of gravity. Overall I think MM is doing a handful of clever shortcuts to give a pretty realistic "feel" of water to the player without bogging down the engine with any real fluid dynamics. My guess would be that if there's some not-at-all-like-the-real-world forces at play, they are more likely to be found underwater than in the basic gravity model, but I'm just thinking out loud. Sackboy himself has always had magic force generating powers (like keeping a pendulum he's hanging from to one side in spite of gravity) so who knows.

2010-01-03 04:23:00 Author: LittleBigDave Posts: 324

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So I misspoke slightly earlier as I was going from memory...the weird result where one object sinks and yet when shrunk floats was not with equal size blocks of wood and metal, but rather with a 12.5x10x1 block of wood glued to a 10x10x1 block of metal. That one sinks but when shrunk down to about 1/16 size (to the smallest with small grid on) it gradually floats up.

2010-01-03 06:37:00 Author: LittleBigDave Posts: 324

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Don't forget about the Tin Foil!

2010-01-03 08:29:00 Author: FreeFlyzz Posts: 265

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i used Glass and Stone and it stayed neutral, Until i swam into it, then it began to behave like Pink Floaty, But out of water pink floaty

2010-01-05 14:08:00 Author: Kern Posts: 5078

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Thinking back to grade 7 physics, something with a larger surface area is more likely to float. Oh, and the "wavy X axis"? water is never perfectly still. I'm still confused, though, because the smaller object floated... and surface area is relative to weight. Oh, no idea...

2010-02-19 22:12:00 Author: nabbott707 Posts: 4

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My seventh-grade teacher taught us a song to remember whether something will float: "Mass divided by volume, Mass divided by volume, Mass divided by volume, Mass divided by volume, Mass divided by volume, Mass divided by volume, Mass divided by volume, Mass divided by volume..." ...Which means, that the less material something is made out of (but is still the same size), the more likely it will float. For example, a hollow wooden block is more likely to float than a solid wood block of the same size.

2010-02-19 22:23:00 Author: Frinklebumper Posts: 941

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What kind of material will float submerged (like you would use to make fish?0

2010-02-20 06:46:00 Author: Ragfell Posts: 729

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What kind of material will float submerged (like you would use to make fish?0 LOL Fish aren't made of a certain material that they float underwater, they contain a "swim bladder" filled with air which they extract from the surrounding water. They regulate the amount of air in the swim bladder to stay stationary, much as a submarine would close and open its ballast tanks to change its average density. And as for the X-movement in water, that I think is a deliberate side-effect added to upthrust, and is only there to allow for more realistic physics without having to overload the engine with a complex new water physics model.

2010-03-05 22:19:00 Author: Holguin86 Posts: 875

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What kind of material will float submerged (like you would use to make fish?0 You would need to use a mixture of; Glass and Metal

2010-03-06 09:37:00 Author: Kern Posts: 5078

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I managed to make a neutrally buoyant submarine that was made of metal, glass, wood, polystyrene, two LED lights, and rockets. It wasn't nearly as hard to make as I thought it would be, and I just experimented by cutting and adding materials. With a player in it, though, it moves very slowly toward the surface. It has thrust and launches rockets

2010-03-06 16:09:00 Author: Hibbsi Posts: 203

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I managed to make a neutrally buoyant submarine that was made of metal, glass, wood, polystyrene, two LED lights, and rockets. It wasn't nearly as hard to make as I thought it would be, and I just experimented by cutting and adding materials. With a player in it, though, it moves very slowly toward the surface. It has thrust and launches rockets why not make it emit a really small amount of metal? so it stays buoyant? (I SPELT IT RIGHT!)

2010-03-06 19:24:00 Author: Kern Posts: 5078

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why not make it emit a really small amount of metal? so it stays buoyant? (I SPELT IT RIGHT!) Maybe, I haven't worked on that submarine in over a month, but I might go do that just because I can.

2010-03-06 20:59:00 Author: Hibbsi Posts: 203

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Ishould really grab my variable bouyancy sub from the beta. It has logic systems to vary between more bouyant that water, equal bouyancy to water, less bouyant that water... so it can mimic the real characteristics of a submarine dving / surfacing / cruising underwater.

2010-03-07 01:26:00 Author: rtm223 Posts: 6497

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Ishould really grab my variable bouyancy sub from the beta. It has logic systems to vary between more bouyant that water, equal bouyancy to water, less bouyant that water... so it can mimic the real characteristics of a submarine dving / surfacing / cruising underwater. You should....

2010-03-09 19:33:00 Author: Kern Posts: 5078

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Hey. I found out that equal parts metal and wood glued together have neutral buoyancy.

2010-08-02 20:23:00 Author: Unknown User

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