On the power of explosives

[ultimagtr]

It has been said that we have reached the limits of chemical explosive technology. Military's used RDX, TNT, HMX, PETN during WWII which is what they are still using now. A brick wall has been hit in the development of conventional energetic substances. Maybe this is a good thing, the world might be a very different place if explosives were just 5 or 10x more powerful.

Imagine a full size chevy suburban. I estimate that it takes less than 100mL of gasoline to take that beast to 80mph. Now imagine that it crashed into a solid cement wall at that speed. Total devastation, engine block cracked to pieces, steel frame twisted and bent, instant death for any occupants, etc. 100mL of nitroglycerin wouldn't do nearly as much damage, maybe do some damage to bodywork and light structural damage.

In order to get the energy out of the gasoline, you need a highly specialized device know as an engine. And engine works by building on small explosions, as we all know. Gasoline has as a tremendous amount of energy, but it can only give so much output at a time.

The problem of course is not the energy. A pound of butter has more caloric energy than a pound of TNT. The problem is getting all that energy out at once in a powerful explosion. I would estimate a tanker truck has at least at much stored energy as a tactical nuke gives off in an explosion. I will get back to you on the mathematics of that one.

Anyway, someday somebody might figure out how to get out all the energy out of such substances in a explosion. You know the military is working day and night on this. I read a long article in a magazine a while back about how they are working on radioactive explosives that would be many more times more powerful than conventional explosives.

Thanks for reading.

[MH-iforgotmypassword]

1 Gallon gasoline = 124,000 Btu
Tanker truck = 7500 gallons to 9900 gallons
124K*9K(standard tanke)=1 116 000 000 (1 billion btu)

A-bomb = 14 kilotons.
1 kiloton = 4.2 trillion joules.
4.2 trillion joules = 4.2 billion BTU
14*4.2b=59 billion BTU.

And that's a uranium based weapon, similar to current tac-nukes.
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810 calories (nutritional) in a stick of butter,
4 sticks to a pound
3240 calories(nutritional) in a pound of butter
3240k calories (scientific) in a pound of butter
1 calorie = 4.18400 joules
13 556 160 joules/pound butter

kg of TNT = 4.184×10^6 Joules
.45kg = 1 lb
.45*4.184*10^6
1 882 800 joules/pound tnt

TNT has bonds that are easy to break, while for butter this is less true. However, both of these bonds are bonds between atoms, making it somewhat comparable.
Comparing a tanker to a nuclear weapon is different though, as it is comparing intra to inter atomic forces.
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Also, you have to look at force distribution for your truck example - one of the main reasons that the NG wouldn't be as effective is because much of the blast energy would travel into the atmosphere, possibly after blowing through the path of least resistance.

Re: engines needed for gas: FAE

also, last paragraph: could you clarify that a little? I mean, it reads as "the government is working on using nuclear explosions in a bomb" which is far fetched. They would need a special project to do that. A secret one. Named after a portion of a city in an eponymous state.

[asilentbob]

A good portion of the energy from 100ml of gas when its burned as fuel in a truck is lost as heat and the end efficiency is still rather low, yet its still pretty powerful.

Then again 100ml of some bio or chemical weapons could cause much more destruction im sure.

Radioactive things arn't good short term. And bio and chemical weapons have a tendency to have un-forseen consequences. I think that governments are going to move to more kinetic weapons... like satellites with tungsten telephone poles, rocket boosters, rudimentary fins, and a guidance system.

Imagine a moon base accelerating tungsten encased shipping container sized compartments of packed or cast cement towards the earth at high speeds... Thats alot of kinetic energy.

Edit:
And laser/microwave weapons. Like satellite networks that store solar energy and have very good aiming/focusing accuracy.

[ultimagtr]

1 Gallon gasoline = 124,000 Btu
Tanker truck = 7500 gallons to 9900 gallons
124K*9K(standard tanke)=1 116 000 000 (1 billion btu)

A-bomb = 14 kilotons.
1 kiloton = 4.2 trillion joules.
4.2 trillion joules = 4.2 billion BTU
14*4.2b=59 billion BTU.

And that's a uranium based weapon, similar to current tac-nukes.
--------------------------------------------------------------------
810 calories (nutritional) in a stick of butter,
4 sticks to a pound
3240 calories(nutritional) in a pound of butter
3240k calories (scientific) in a pound of butter
1 calorie = 4.18400 joules
13 556 160 joules/pound butter

kg of TNT = 4.184×10^6 Joules
.45kg = 1 lb
.45*4.184*10^6
1 882 800 joules/pound tnt

TNT has bonds that are easy to break, while for butter this is less true. However, both of these bonds are bonds between atoms, making it somewhat comparable.
Comparing a tanker to a nuclear weapon is different though, as it is comparing intra to inter atomic forces.
----------------------------------------------
Also, you have to look at force distribution for your truck example - one of the main reasons that the NG wouldn't be as effective is because much of the blast energy would travel into the atmosphere, possibly after blowing through the path of least resistance.

Re: engines needed for gas: FAE

also, last paragraph: could you clarify that a little? I mean, it reads as "the government is working on using nuclear explosions in a bomb" which is far fetched. They would need a special project to do that. A secret one. Named after a portion of a city in an eponymous state.Thanks for those calculations, I was going to do them myself but I got lazy. 14 kilotons conventional nuke size, not tactical nuke size. I think your standard 'suitcase' bomb is around a kiloton or less, and plutonium based of course. So 14kilotons = 59billion btu, 1 tanker = 1.1billion btu. So a 1.4 kiloton tactical nuke (on the large side) has equivalent btu output to less than 6 tankers (1.1x6= 6.6 vs 5.9 for the nuke). Seems about right.

Butter has waay more power than TNT, but requires a complex digestive system to get the enery out of. The energy is not released in a millisecond or so like TNT. So really not a fair comparison, it is all about breaking down chemical bonds as quickly as possible.

As far as the last paragraph, it was an article I read a long time ago in a magazine. It was really bizarre actually, about how the military had a facility which had a greek letter for a name. It talked about how they were using a bunch of dental xray machines for R&D to hopefully develop this explosive. They were trying to develop a radioactive explosive that would be many times more powerful than conventional HE's. I will try to get more info.

@asilentbob I agree the future is kinetic weapons. What about railguns, I think they might be the next great military achievement.

[delusional_reality]

In order to get the energy out of the gasoline, you need a highly specialized device know as an engine. And engine works by building on small explosions,


I don't mean to be picky but thought you might be interested in the fact that inside the ''combustion'' chamber no detonation explosions occur, only deflagration ''explosions''.
Reason being, engines work on the brayton or constant pressure cycle...a lot of interest is in pulse detonation engines/ based on Humphry cycle..which extract more of the energy of the fuel.

http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000125000004001075000001&idtype=cvips&gifs=yes

[psyco_1322]

Im sorry but I dont think its correct to compare the explosive power of NG to the destructive force of 3 tons of sheet metal hitting a brick wall. Most like the brick wall would loose, being knocked down, but I see for your explanation is was an indestructible wall. Sure the gas got the vehicle moving but it not really responsible for all the damage that happened.

[BoilingLeadBath]

Well, two main reasons:

1) 100 ml NG != 100 ml gasoline
The energy released by reacting 100 ml of the gasoline is several times larger - the hydrocarbon molecules don't have to have their own built-in oxidizer.

2) Energy coupling.
Almost all of the energy created by the NG will be wasted, whereas the engine operates at ~35% or so efficiency, and then (assuming a completely static wall) ALL of this energy is used to damage stuff.

Unfortunately, the popular way of extracting energy from explosions is to confine the explosion with something solid, and then let that solid mass deposit that energy into the target - see guns, grenades, explosively formed penetraters, perhaps even shaped changes (depending upon how you wish to view them).
Also known as shrapnel. Hobbyists aren't trying to kill people, so this is a bad thing.

[wolfy_9005]

Shaped charges increase the power by alot.....although you need to stick em flat, and not like the arabs are doing(casing them in metal sharps).

All depends on placement as to how much damage it does aswell. 100kg of TNT might blow up a car, or it could blow up a whole city block.

And an explosion doesnt have much(any?) mass behind it.

A car @ 2000kg moving @ 80mph(~130kmh) = 260,000kg force.(correct? not too good with my physics, but pretty sure it's v x m = F or w.e). Or .25kilotons. Basically a weak tactical nuclear weapon.

[asilentbob]

100kg of TNT (cast) would only take up about 2.2 cubic ft... thats not going to "blow up" a whole city block.

[Declan]

Some of the physics in this thread make me want to cry...

First of all, force is mass times ACCELERATION, not velocity. And that's not how you do it, it's generally to say "force X applied to mass M gives rise to acceleration A".

What you're looking for is kinetic energy, which is K = .5m*v^2. What you might've been thinking of is impulse, which is F * delta t = delta p, where p is the momentum. It's a way to calculate forces on objects that are transferring momentum.

There are a bunch of things wrong with your analogy. For instant, 100ml could do a decent bit of more damage (still not destroy a car but still) if it was encased. You're also giving a few freebies to the gasoline side, the oxidizer that you didn't take into account and also the brick wall which provides a very high normal force, allowing the KE to actually be transferred to something other than the ground.

Some of the things I would guess at being possible weapons in the future: railguns, crazy specific biological weapons (that could just kill people with the right genes or something), and things along the lines of that weird weapon the military was saying "Didn't hurt people", the one that was basically a microwave gun. Don't know much about it.

[wolfy_9005]

Velocity is speed, and acceleration is speeding up....

but w.e i never did physics.

[MH-iforgotmypassword]

Some of the things I would guess at being possible weapons in the future: railguns, crazy specific biological weapons (that could just kill people with the right genes or something), and things along the lines of that weird weapon the military was saying "Didn't hurt people", the one that was basically a microwave gun. Don't know much about it.

They have a microwave gun, and then they have something similar that generates plasma which targets nociceptors.
http://www.newscientist.com/article.ns?id=dn7077

[Giggles_The_Panda]

They would need a special project to do that. A secret one. Named after a portion of a city in an eponymous state.

This. I lol'd

[Nereth]

engines work on the brayton or constant pressure cycle

I think the engines the op was referring to were mostly otto cycle ICEs.

For clarification to others, brayton cycle = turbines, otto cycle = what your car most likely is, and otto cycles are not at all constant pressure.

[SLP]

All of the damage done by the wall is in one dimension. The explosive is generally omnidirectional.

So the amount of damage the explosive is doing that is the same as the wall is only the cubic root of the explosive's total damage

If the explosive was in the same dimension and direction the wall is causing damage, then the explosive will cause a more comparable amount of damage in that dimension.