Grease spell confusion

[Saeviomagy]

Again, my point is that the cup does not catch fire because of it's absorptivity, and has nothing to do with heat transfer and everything to do with the properties of flammability of the contents. A paper cup holds water how? Once filled, water molecules soak into the fibers of the paper, and the paper expands slightly, sealing in water better than if it contracted. If you let the paper cup sit for hours you will see the cup leaking. No, it is not condensation, and you can try it with room temperature water.
What is happening with the cup under the bunsen burner then? The heat is being transferred to the water via conductance and radiance, yes; but by no means does this have anything to do with the flammability of the cup but the flammability of the water in the paper fibers, of which happens to be nil. If you boiled the water in the cup, the cup will still not ignite. If you sealed the cup and produced steam in the cup, the heat will drive the steam upwards until the bottom is dry enough for the fire to catch.

"Dude, you are so wrong! I saw it happen, man, I was there!"

That's great, I'm sure it did, and perhaps that's the logic of your teacher, but I'm glad I studied the mechanics of materials and heat transfer a little better than him/her. Next time, ask your teacher to fill a cheap plastic container (not heat resistant) with water and try the same trick. The water may prevent the plastic from getting hot for a little bit, but the plastic will certainly melt before the water boils. Why didn't the water absorb the heat then?

edit: Sorry, don't mean to hijack the thread, but I feel like I have to defend RL physics a bit.

You're flat-out wrong.

Think hard. Why is wet paper not flammable? Is the paper still there? Yes. So why is it suddenly not burning? Because there's some water nearby? What does that have to do with it?

What spectacular property does water have that it stops chemical reactions in molecules near it?

What is happening when the wet cup gets heated?

The water turns to steam. You said so yourself.

What do you suppose is required to turn water into steam. I'll tell you - heat.

If that heat is turning water into steam, then it's no longer available to ignite the paper cup.

Furthermore, the act of water turning to steam uses up more energy than raising the temperature of the water from 99 to 100 degrees.

Additionally, the evaporating water takes some of the heat with it.

I would expect that if this experiment doesn't work in a plastic container, then it is due to one or both of the following factors:

1. Plastic is a good insulator, and in the average plastic container, theres significantly more plastic between the heat source and the water than with the paper container.
2. The melting point of the plastic in question is lower than the boiling point of water.

Given that this principle is widely known and applied (ever wondered what a heatsink is for?), I think you may want to hit your physics books a bit more.

Also Conaill - your examples don't work because of the amount of air. It works because of the temperature that the material can be raised to. If you take a 1kg block of iron, and file it into a powder, then the amount of energy required to ignite all of it is still the same as the amount of energy required to ignite it when it was a block. The real difference is that the iron as a powder cannot conduct heat away quickly - instead of heating the entire iron block, you heat only the parts exposed to flame, and they therefore get much hotter, then reach their activation point and start combusting. The combusting iron then applies heat to the powder nearest it etc. While it is true that starving a reaction of oxygen will cause it to fail, starving a reaction of heat will cause the same thing.

 

[Camarath]

So, paper cranes created by a spell are immune to fire? That is a nifty trick.

What is the paper made out of? Is it real paper (non-magical)? Does the spell say it reacts like normal (wood or hide based) paper?

I am not adding anything that wasn't there, I am only pointing out something that others might have overlooked. Grease burns if it gets hot enough. The question is only heat and oxygen. If oxygen is an issue, you have a bigger problem than the grease spell.

The definition of grease
Main Entry: grease
Pronunciation: 'grEs
Function: noun
Etymology: Middle English grese, from Old French craisse, graisse, from (assumed) Vulgar Latin crassia, from Latin crassus fat
Date: 13th century
1 a : rendered animal fat b : oily matter c : a thick lubricant

This definition (subpart c) does not preclude many substances that are not flammable for being considered greases. Silicone Grease for example does not oxidize or burn.

Grease burns. I am only looking objectively at the spell.

Iron will also burn in the right conditions. Yes, Iron can under go that exothermic oxidation reaction called combustion.

No, iron is not flammable. At high temperatures, it melts. Over time, it oxidies. These are not the same. Take heat away, the iron hardens. The grease keeps burning.

The U.S. Occupational Health and Safety Administration (OSHA) defines a flammable liquid as "any liquid having a flash point below 100 deg. F. (37.8 deg. C.), except any mixture having components with flash points of 100 deg. F. (37.8 deg. C.) or higher, the total of which make up 99 percent or more of the total volume of the mixture. Flammable liquids shall be known as Class I liquids."

By OSHA's definition neither grease (most anyway) or iron are flammable. If what you mean by flammable is capable of combustion then both grease (most) and iron are flammable in the right circumstances. Also how much heat are you removing from the grease? If the loss of energy to the environment is high enough combustion will cease.

Your example is rather silly. I am not talking about rocket science here.

It was meant to be. IIMO presuming that the grease would be flammable and extrapolating game mechanics out of the asumption, wile not calling them House Rules, is rather silly.

 

[Camarath]

Again, my point is that the cup does not catch fire because of it's absorptivity, and has nothing to do with heat transfer and everything to do with the properties of flammability of the contents.

Minor nitpicking point, I don't think Absorptivity is the word you were looking for.

Main Entry: ab·sorp·tiv·i·ty
Pronunciation: &b-"sorp-'ti-v&-tE, -"zorp-
Function: noun
Inflected Form(s): plural -ties
Date: circa 1859
: the property of a body that determines the fraction of incident radiation absorbed by the body

 

[Pielorinho]

"Dude, you are so wrong! I saw it happen, man, I was there!"

That's great, I'm sure it did, and perhaps that's the logic of your teacher, but I'm glad I studied the mechanics of materials and heat transfer a little better than him/her.

Other people have explained the errors in your understanding better than I can, but you're "correcting" me, so I want to chip in. My understanding of this is correct, and I've cited two different sources explaining how the experiment works. Google "burn paper cup water," and you'll find dozens of Web sites detailing this (very common) physics demonstration and explaining how it works.

If the common understanding of this experiment is incorrect, surely you'll be able to cite a few credible Websites that take your side in the argument, that seriously suggest it's soggy paper and not heat transference that makes the experiment work. Otherwise, a sheepish grin and an "oops" would make a fine next contribution to the thread .

Daniel

 

[LokiDR]

What is the paper made out of? Is it real paper (non-magical)? Does the spell say it reacts like normal (wood or hide based) paper?

With no definition besides "paper" you should conclude that it is flamable. Only if the spell states that it is not flamable do you assume it isn't.

The definition of grease
Main Entry: grease
Pronunciation: 'grEs
Function: noun
Etymology: Middle English grese, from Old French craisse, graisse, from (assumed) Vulgar Latin crassia, from Latin crassus fat
Date: 13th century
1 a : rendered animal fat b : oily matter c : a thick lubricant

This definition (subpart c) does not preclude many substances that are not flammable for being considered greases. Silicone Grease for example does not oxidize or burn.

If your fantasy setting has silicone gel, no the spell is not inherantly flamable.

Iron will also burn in the right conditions. Yes, Iron can under go that exothermic oxidation reaction called combustion.

Everything burns. Everything.

That said, I will never get an iron ingot to light on fire with a blowtorch. You would have to do something like powerder it. That is why the iron body example is insanely stupid and masking the point. Many forms of grease will take fire just in the presence of high heat.

The U.S. Occupational Health and Safety Administration (OSHA) defines a flammable liquid as "any liquid having a flash point below 100 deg. F. (37.8 deg. C.), except any mixture having components with flash points of 100 deg. F. (37.8 deg. C.) or higher, the total of which make up 99 percent or more of the total volume of the mixture. Flammable liquids shall be known as Class I liquids."

By OSHA's definition neither grease (most anyway) or iron are flammable. If what you mean by flammable is capable of combustion then both grease (most) and iron are flammable in the right circumstances. Also how much heat are you removing from the grease? If the loss of energy to the environment is high enough combustion will cease.

Some greases are flamable. By that definition, by the way, paper is not flamable, neither are cotton balls or lint. In short, that definition isn't useful for showing "flamable".

The circumstance is a "a large puddle". Grease is flamable, iron isn't. I am not arguing every possible circumstance, only the ones mentioned by grease and iron body.

It was meant to be. IIMO presuming that the grease would be flammable and extrapolating game mechanics out of the asumption, wile not calling them House Rules, is rather silly.

It isn't a house rule? Great, so you agree. Thanks for clearing that up.

Your example of iron body obuscates the point. A large mass of solid iron will not burn. A large mass of many "greases" will. A torch will never light a piece of iron. It might light a pile of grease. Most any grease that fits in a fantasy setting will ignite with enough heat, in the manor of crisco or lard.

There is no balance issue with saying grease emulates crisco. It makes the spell more interesting. It allows the players to be inventive. And it reflects a realism that helps the game.

 

[Pielorinho]

Many forms of grease will take fire just in the presence of high heat.

I'm very close to saying, "nuh uh," again. instead, why not tell us of your experience exposing puddles of normal grease to high heat and seeing the burst into flame? I'm convinced that normal greases -- i.e., ones commonly rendered from plant or animal sources -- do not behave like this, for the reasons I've given above; but I'm willing to see evidence to the contrary.

Daniel

 

[LokiDR]

Other people have explained the errors in your understanding better than I can, but you're "correcting" me, so I want to chip in. My understanding of this is correct, and I've cited two different sources explaining how the experiment works. Google "burn paper cup water," and you'll find dozens of Web sites detailing this (very common) physics demonstration and explaining how it works.

You are both saying it is heat transfer, but Pielorinho seems to think it has nothing to so with water perminating the surface where MarauderX thinks that is the key.

There is a way to solve this problem. Make a container of a non-insulating, non-water-permiable material that melts/burns at a low temperature. Thin plastic or lead would be good options.

You will find, I think, that materials other than paper will spout holes and leak long before the water boils away. The heat transfer only works in the paper cub because the water is right at the surface of the material. The water then soaks up the heat/evaportates. If the water isn't in the material (non permiable) the heat transfer will not be fast enough for the water to take all the heat and prevent the container from melting.

 

[Pielorinho]

You are both saying it is heat transfer, but Pielorinho seems to think it has nothing to so with water perminating the surface where MarauderX thinks that is the key.

There is a way to solve this problem. Make a container of a non-insulating, non-water-permiable material that melts/burns at a low temperature. Thin plastic or lead would be good options.

MarauderX is wrong, unfortunately . Check out the links I cited earlier, or go to your own favorite page of physics experiments and look for this one. You'll find that it works equally well on wax-coated paper cups, eliminating the possibility that it's soggy paper producing the effect.

If you're still curious, you can empty water from a paper cup and immediately trying to light it. A shiny new quarter says you'll find the just-emptied cup almost as easy to light as a never-moistened cup: that's because the just-emptied cup no longer can transfer the heat to the water within.

This is pretty basic physics, and is widely known and accepted. A quirk of heat transference is responsible for anyone's ability to walk on red-hot coals without getting hurt, and similarly responsible for nobody's ability to walk in ankle-deep boiling water without getting hurt. If you know and understand your physics, this is uncontroversial.

If you disagree, let's see some evidence to the contrary. Note that Marauder has so far not produced any such evidence; can you?

Daniel

 

[Pielorinho]

Here's a similar experiment involving no water at all. Place a metal rod and wooden dowel (of equal thickness) end-to-end, and wrap a piece of paper tightly around them so that it covers equal amounts of the wooden dowel and the metal rod. Hold them over a bunsen burner.

The paper over the wood won't burn right away, since paper conducts heat so well; but as the wood heats up, it'll begin to char the paper. Wood doesn't conduct heat.

Metal does, however, so the paper surrounding the metal won't burn at all, not until it's been in the fire for a really really long time (i.e., long enough for the metal rod itself to get really hot).

Convinced yet? Or is the paper getting soggy from being so close to metal?

Daniel

 

[LokiDR]

I'm very close to saying, "nuh uh," again. instead, why not tell us of your experience exposing puddles of normal grease to high heat and seeing the burst into flame? I'm convinced that normal greases -- i.e., ones commonly rendered from plant or animal sources -- do not behave like this, for the reasons I've given above; but I'm willing to see evidence to the contrary.

Daniel

Fair enough. The simplest example is oil. I have added oil to fires to burn it off. In small fires it didn't catch, but in larger fires there was a sudden flare up for a few moments. Another example was cooking sausages out on a grill. Squeeze the saussage and they light on fire. You have burned saussage for dinner, but that is another problem. Finally, multiple years of boyscouts has taught me that lots of grease+open fire = problems. I watched a guy name Andy scorch his hand adding butter to a meal.