# Is it possible to build a kinetic energy bomb?
**URL:** https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112
**Category:** Factual Questions
**Created:** [September 20, 2004, 10:11am UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112 "2004-09-20T10:11:14Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@Liberal](https://boards.straightdope.com/u/Liberal)
#### Post date: [September 20, 2004, 10:11am UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/1 "2004-09-20T10:11:14Z")
I was thinking of asteroids and the incredible amount of energy that is unleashed by a few tons of rock smashing into the earth at 40 times the speed of sound. Would it be possible to build kinetic energy bombs on a smaller scale than that, that would destroy small countries or large cities without the hassle of nuclear fallout? Would the ballistics (e.g., the trajectory through the atomsphere) be too unreliable? Would it be hard to accelerate sufficient mass to sufficient speed? Or is it feasible?
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### Author:  [@SPOOFE](https://boards.straightdope.com/u/SPOOFE)
#### Post date: [September 20, 2004, 10:20am UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/2 "2004-09-20T10:20:49Z")
Sure. You can use the [Oh My God particle](http://www.fourmilab.ch/documents/ohmygodpart.html) as an example… a single proton with the amount of kinetic energy as a brick falling on your toe.
The two factors that go into determining kinetic energy are mass and velocity, so if you want to do it without a lot of mass, you need a lot of velocity.
As far as “would it be worth it”, I dunno. A railgun can get a tiny object going pretty damned fast, but they’re pretty infeasible as weapons. On the other hand, it’s no picnic getting an asteroid moving at any appreciable velocity, either. I’d say that, for now and for the foreseeable future (lacking any huge leaps in propulsion or energy-producing technology), explosives and nukes and such are still our best ways to cause lots of stuff to go kablooie.
“Kablooie” being used as a scientific term, here, of course…
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### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [September 20, 2004, 10:35am UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/3 "2004-09-20T10:35:44Z")
Larry Niven and Jerry Pournelle have written quite a lot about an idea called _Thor_, where (oversimplifying) iron rods could be dropped from orbit - essentially artificial meteorites. They would do a fair bit of damage without using any explosives at all, but I think the scope of this project was to replace conventional bombing, so the target size would be relatively small - individual structures and complexes, rather than entire cities or small countries.
If you wanted to wipe out larger areas, you could probably (in the sense that it isn’t stupidly impossible, that is) divert a near-earth orbit object so that it hit your target; the advantage here is that you could be dealing with something that already has a great deal of initial velocity already (so the yield would be higher for a given size of object), but that in turn would make targetting more delicate a task.
The BIG disadvantage of trying something on that sort of scale is that it appears to be something on that sort of scale that wiped out the dinosaurs - not much point winning the war if you screw the entire planet (well, I don’t think so, anyway, but I suppose it might make sense in a _Mutual Assured Destruction_ scenario, if ‘sense’ isn’t an entirely inappropriate term).
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### Author:  [@mks57](https://boards.straightdope.com/u/mks57)
#### Post date: [September 20, 2004, 12:22pm UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/4 "2004-09-20T12:22:37Z")
The USAF used concrete bombs to attack Iraqi air defense installations before the most recent war. See [http://www.fas.org/news/iraq/1999/10/991007-iraq.htm](http://www.fas.org/news/iraq/1999/10/991007-iraq.htm). In this case, the motivation was to limit collateral damage to civilans.
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### Author:  [@Bosda\_Di\_Chi\_of\_Tricor](https://boards.straightdope.com/u/Bosda_Di_Chi_of_Tricor)
#### Post date: [September 20, 2004, 12:26pm UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/5 "2004-09-20T12:26:28Z")
There is a technology that uses solid projectiles, propelled by expanding gasses, compressed gasses, or magnetic fields, to deliver kinetic energy damage to targets.
I believe that they are called “guns”.
You _must_ have read about them, it was in _all_ the papers. :dubious: :rolleyes:
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### Author:  [@Finagle](https://boards.straightdope.com/u/Finagle)
#### Post date: [September 20, 2004, 1:03pm UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/6 "2004-09-20T13:03:08Z")
> [@Bosda Di'Chi of Tricor](#):
>
> There is a technology that uses solid projectiles, propelled by expanding gasses, compressed gasses, or magnetic fields, to deliver kinetic energy damage to targets.
>
> I believe that they are called “guns”.
>
> You _must_ have read about them, it was in _all_ the papers. :dubious: :rolleyes:
A careful reading of the OP might have indicated that the question being asked concerned a scale somewhat larger than guns.
The nice thing about kinetic weapons like Thor, or even the rocks in “The Moon is a Harsh Mistress” is that they use gravity to accelerate the mass in question. And gravity is pretty much free and very, very reliable. The bad thing is that you have to get the mass to the right point in the gravity well, and that’s where things fall apart right now. At the moment, it’s still thousands of dollars a pound to put something in orbit. So a Thor-like weapon would cost as much as a cruise missile just to take out one tank. Meanwhile, any jamoke in Iraq seems to be able to pick up a secondhand RPG for chump change.
Bigger kinetic energy weapons obviously requires more infrastructure. Is it cost effective constructing a moonbase or diverting an asteroid just to deliver a smackdown to some planet-based opponent? Very unlikely, unless the infrastructure was already in place. The only scenario I cn think of is if you wanted to sneakily destroy a single city – then you could opportunistically divert a passing Earth grazer – “detect” it at the last moment, warn everyone at slightly after the last moment, then shake your head sadly as it plummeted to Earth, wreaking havoc. But that would require a huge coverup and it’s hard to imagine the motivation.
None of this really addresses the technical feasibility of moving a large mass and aiming it with precision – tasks which are probably do-able but beyond our present level of technology.
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### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [September 20, 2004, 1:14pm UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/7 "2004-09-20T13:14:08Z")
How about another kind of kinetic energy weapon; a spherical bomb casing that contains what is essentially a massive flywheel, suspended on frictionless bearings (the real-world construction of which is left as an exercise for the reader) and a system of gimbals, so that it doesn’t start exerting torque on the plane when it tries to bank etc. Spin the flywheel up to some stupidly fast speed and drop the whole thng on the enemy base.
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### Author:  [@Finagle](https://boards.straightdope.com/u/Finagle)
#### Post date: [September 20, 2004, 2:00pm UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/8 "2004-09-20T14:00:32Z")
> [@Mangetout](#):
>
> How about another kind of kinetic energy weapon; a spherical bomb casing that contains what is essentially a massive flywheel, suspended on frictionless bearings (the real-world construction of which is left as an exercise for the reader) and a system of gimbals, so that it doesn’t start exerting torque on the plane when it tries to bank etc. Spin the flywheel up to some stupidly fast speed and drop the whole thng on the enemy base.
What does this buy you that explosives won’t? It sounds wickedly expensive, the energy to spin up the flywheel isn’t supplied by gravity or any other free source, and you can’t really aim it. Practically speaking, if we could build that kind of flywheel, we’d be using it for regenerative braking applications.
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### Author:  [@Polycarp](https://boards.straightdope.com/u/Polycarp)
#### Post date: [September 20, 2004, 2:23pm UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/9 "2004-09-20T14:23:33Z")
> [@Mangetout](#):
>
> Larry Niven and Jerry Pournelle have written quite a lot about an idea called _Thor_, where (oversimplifying) iron rods could be dropped from orbit - essentially artificial meteorites. They would do a fair bit of damage without using any explosives at all, but I think the scope of this project was to replace conventional bombing, so the target size would be relatively small - individual structures and complexes, rather than entire cities or small countries.
>
> If you wanted to wipe out larger areas, you could probably (in the sense that it isn’t stupidly impossible, that is) divert a near-earth orbit object so that it hit your target; the advantage here is that you could be dealing with something that already has a great deal of initial velocity already (so the yield would be higher for a given size of object), but that in turn would make targetting more delicate a task.
> The BIG disadvantage of trying something on that sort of scale is that it appears to be something on that sort of scale that wiped out the dinosaurs - not much point winning the war if you screw the entire planet (well, I don’t think so, anyway, but I suppose it might make sense in a _Mutual Assured Destruction_ scenario, if ‘sense’ isn’t an entirely inappropriate term).
Precisely. This was an element of the Strategic Defense Initiative of the Reagan era (which was first scoped out at planning sessions at the Niven home – some of their non-fiction writings describe a bit about this.)
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### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [September 20, 2004, 2:33pm UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/10 "2004-09-20T14:33:27Z")
> [@Finagle](#):
>
> What does this buy you that explosives won’t? It sounds wickedly expensive, the energy to spin up the flywheel isn’t supplied by gravity or any other free source, and you can’t really aim it. Practically speaking, if we could build that kind of flywheel, we’d be using it for regenerative braking applications.
All good points; I only mentioned it because it crossed my mind that kinetic energy doesn’t necessarily have to be delivered in vector format.
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### Author:  [@ftg](https://boards.straightdope.com/u/ftg)
#### Post date: [September 20, 2004, 2:35pm UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/11 "2004-09-20T14:35:32Z")
Yet Another Downside: The country you’re targetting says “Uncle” 3 hours before your Big Rock is about to hit them. What do you do?
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### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [September 20, 2004, 2:48pm UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/12 "2004-09-20T14:48:07Z")
> [@ftg](#):
>
> Yet Another Downside: The country you’re targetting says “Uncle” 3 hours before your Big Rock is about to hit them. What do you do?
Send for Bruce Willis.
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### Author:  [@mks57](https://boards.straightdope.com/u/mks57)
#### Post date: [September 20, 2004, 3:43pm UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/13 "2004-09-20T15:43:34Z")
> [@Finagle](#):
>
> What does this buy you that explosives won’t? It sounds wickedly expensive, the energy to spin up the flywheel isn’t supplied by gravity or any other free source, and you can’t really aim it. Practically speaking, if we could build that kind of flywheel, we’d be using it for regenerative braking applications.
It’s an interesting idea. I used to hear folk stories about the damage that could be caused by high-speed gyros and rotating drums that escaped their enclosures. The stories usually said that anything that got in the way of the gyro/drum was toast. I don’t know if any of those stories were true. Still, the idea of that much energy being stored in small piece of rotating metal is intriguing.
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### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [September 20, 2004, 4:06pm UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/14 "2004-09-20T16:06:50Z")
> [@SPOOFE](#):
>
> …a single proton with the amount of kinetic energy as a brick falling on your toe.
That’s rather imprecise, isn’t it? Clearly, a brick falling from 100 feet up has more energy than a brick falling from 6 feet. A better analogy is the one that immediately follows: that the particle had the energy of a baseball travelling at 55 MPH.
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### Author:  [@Paul\_in\_Qatar](https://boards.straightdope.com/u/Paul_in_Qatar)
#### Post date: [September 20, 2004, 4:19pm UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/15 "2004-09-20T16:19:55Z")
I for one take exception to the idea of using gerbils, even frictionless ones, in any weapon of war. Very simply, animals are not part of our fight. They cannot volunteer and to force them to take part in a human war is simply wrong.
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### Author:  [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)
#### Post date: [September 20, 2004, 4:24pm UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/16 "2004-09-20T16:24:30Z")
> [@ftg](#):
>
> Yet Another Downside: The country you’re targetting says “Uncle” 3 hours before your Big Rock is about to hit them. What do you do?
“Yeah? Too late…you embarrased me in front of my woman.”
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### Author:  [@Polycarp](https://boards.straightdope.com/u/Polycarp)
#### Post date: [September 20, 2004, 4:34pm UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/17 "2004-09-20T16:34:33Z")
> [@Paul in Saudi](#):
>
> I for one take exception to the idea of using gerbils, even frictionless ones, in any weapon of war. Very simply, animals are not part of our fight. They cannot volunteer and to force them to take part in a human war is simply wrong.
That’s what the lube is for – to make them frictionless. Besides, the Security through Selective Service of Rodents (SSSR) Act stipulates that they can be involuntarily called up for combat duty when Homeland Security requires it! 😉
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### Author:  [@Random](https://boards.straightdope.com/u/Random)
#### Post date: [September 20, 2004, 5:06pm UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/18 "2004-09-20T17:06:13Z")
> [@Paul in Saudi](#):
>
> I for one take exception to the idea of using gerbils, even frictionless ones, in any weapon of war. Very simply, animals are not part of our fight. They cannot volunteer and to force them to take part in a human war is simply wrong.
Communist! Every true American supports our gerbil troops.
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### Author:  [@Squink](https://boards.straightdope.com/u/Squink)
#### Post date: [September 20, 2004, 6:39pm UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/19 "2004-09-20T18:39:03Z")
> [@Mangetout](#):
>
> All good points; I only mentioned it because it crossed my mind that kinetic energy doesn’t necessarily have to be delivered in vector format.
Weren’t some of the dam busters used in WWII designed to spin, so that when they sank to the bottom of the reservior behind a targeted dam, they’d go zipping along the bottom until they struck the dam?
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### Author:  [@ouryL](https://boards.straightdope.com/u/ouryL)
#### Post date: [September 20, 2004, 6:44pm UTC](https://boards.straightdope.com/t/is-it-possible-to-build-a-kinetic-energy-bomb/265112/20 "2004-09-20T18:44:31Z")
> [@Paul in Saudi](#):
>
> I for one take exception to the idea of using gerbils, even frictionless ones, in any weapon of war. Very simply, animals are not part of our fight. They cannot volunteer and to force them to take part in a human war is simply wrong.
Unless they were \*evil \*gerbils!!
:eek: 😃
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