Physics in the News

Dry ice bombs were in the news, with two having gone off at LAX. A bit of a surprise that these haven’t been on the radar much, seeing as they don’t have a chemical signature that could be sniffed out, and have no moving parts. When they blow is not really controllable, but the mechanism is simple — the ice sublimates and pressure builds up. Since a mole of an ideal gas wants to take up 22.4L at STP, while the solid takes up negligible volume. Since the volume is restricted, the pressure builds as more gas accumulates, until the container fails. Boom.

What Is a Dry-Ice Bomb?

It’s noted that such devices are illegal, but when I ran across a story about a teen getting in trouble for doing this in his backyard a while back, the law was stated (or perhaps paraphrased) in such a way that it would make any carbonated beverage illegal. I have to hope most laws are written better than that. It’s rare, but soda bottles can explode, and small amounts of dry ice in containers can be interesting. Context, i.e. the amount of material, matters, much like how the dose makes the poison.

I Don't Like Mondays

Today was a Very Bad Day™, in a depressingly long and growing list of Very Bad Days™. And while there are bound to be proclamations of “it’s too soon to talk about the implications” countered by “if not not now, when?” and so forth, and also some shooter(s) was/were (religion) and (ethnicity) and this has profound implications because of (generalization and/or inappropriate extrapolation), that discussion really doesn’t interest me right now, because we don’t know everything yet.

Of more immediate import to me is the one certain fact: that we don’t know everything yet. That was true all day, as the stories poured out — they were sketchy and often wrong. One shooter, two shooters, three shooters — the number kept changing. One shooter was down, and then that was withdrawn, and then confirmed, but nobody could say if “down” meant dead or arrested. Shooting at Bolling AFB was reported, and then dismissed as being false.

Information dissemination is fast. Twitter and internet news were reporting this very soon after it started. Information collection is slow, and since it’s also imperfect it requires confirmation, making it even slower. And this is one things that tends to get glossed over in the aftermath. That while all of this was going on, we didn’t really know what was happening. It was true after the Boston Marathon bombing and manhunt, and it was true in all of the other incidents before that. If you are going to get involved in any sort of discussion, don’t fall prey to the notion that anyone had more than scant knowledge, or that anything about this should have been obvious. That’s hindsight bias.

(one note, since you may not be familiar with DC at all: I don’t work at the navy yard. Emotions aside, in the grand scheme of things this event only had a minor impact on my day, in that we were in a heightened security situation)

PSA: Hollywood is Not Real

A Public Service Announcement on Guns and Bullets

What I saw there, while interesting from a mildly voyeuristic point of view, disturbed me in two ways. The first, and obvious one, was that I was upset that this was happening in my country, again. The second was concern, because it was really evident from some of the footage, that my fellow Americans watch way too much television and thus have a false understanding about bullets. So this afternoon’s public service announcement is to try and prevent possible harm that might otherwise be avoided.

An excellent article, as far as I can tell, with one caveat:

Power, with guns, is dictated by physics. As my father the physicist taught me at way too early of an age, F = M x A. Force = Mass x Acceleration. The striking, or penetrating, power of the bullet is determined by how heavy (mass) it is, multiplied by how fast it is moving. Thus, a small bullet, moving at extreme speeds, can cause a lot of damage. A large bullet can move at much slower speeds, and cause the same damage. All other things being equal, however, the higher the speed, the greater the penetration. Now, that word “penetration” is one you should think about.

He’s not describing F = ma here. Mass*velocity gives the momentum, but one also needs to look at the kinetic energy. A small bullet moving at some speed has the same momentum as a bullet of twice the mass, moving at half the speed, but it also has twice the energy, and that has some effect on penetration. The salient point, I believe, is that you don’t want that energy deposited in your body, and that’s true regardless of which case you have.

Boom, Boom, Out Go the Lights

BREAKING: Huge Meteor Blazes Across Sky Over Russia; Sonic Boom Shatters Windows [UPDATED]

Apparently, at about 09:30 local time, a very big meteor burned up over Chelyabinsk, a city in Russia just east of the Ural mountains, and about 1500 kilometers east of Moscow. The fireball was incredibly bright, rivaling the Sun! There was a pretty big sonic boom from the fireball, which set off car alarms and shattered windows. I’m seeing some reports of many people injured (by shattered glass blown out by the shock wave). I’m also seeing reports that some pieces have fallen to the ground, but again as I write this those are unconfirmed.

That's a Big Twinkie

I’ve been reading about some people expressing frustration that they are still in a bad way after hurricane Sandy — no power, long lines for gasoline, etc. Yes, it’s tough and you have my sympathy and empathy (90 hours without power this summer after being hit with a derecho gives me an inkling of the troubles)

But this was no small thing. The NOAA website discusses the energy released in a hurricane

It turns out that the vast majority of the heat released in the condensation process is used to cause rising motions in the thunderstorms and only a small portion drives the storm’s horizontal winds.

A typical hurricane releases an average of 6 x 10^14 Watts of power — it’ll be higher where there is more rainfall — which is 200 times the electrical energy generation in the world. The wind energy is a fraction of a percent of that, but is still half the world’s electricity generation level. And Sandy was bigger, so the numbers will be higher. All of that, focused on the mid-Atlantic/Northeast coastal areas.

The point is that there was a lot of fury unleashed last week, and it takes some time to recover from that. Gasoline in short supply indicates some of the logistical problems going on. A lot of people, requiring a lot of energy, all of it needing to be imported somehow. All of the behind-the-scenes things we take for granted, until a disruption occurs.

That Other Steroid Problem

It’s Global Warming, Stupid

An unscientific survey of the social networking literature on Sandy reveals an illuminating tweet (you read that correctly) from Jonathan Foley, director of the Institute on the Environment at the University of Minnesota. On Oct. 29, Foley thumbed thusly: “Would this kind of storm happen without climate change? Yes. Fueled by many factors. Is storm stronger because of climate change? Yes.” Eric Pooley, senior vice president of the Environmental Defense Fund (and former deputy editor of Bloomberg Businessweek), offers a baseball analogy: “We can’t say that steroids caused any one home run by Barry Bonds, but steroids sure helped him hit more and hit them farther. Now we have weather on steroids.”