Entries by Colin Turner

Every year I attempt to visit my old PhD supervisor Brian McMaster (old in the sense that my PhD is now a thing of the past, I am making no reference to the man in question!) at Christmas time to have a quick natter and exchange gifts. I was squeezed for time this year since I also had to hire a gown from Queen's to attend an event for the University of Ulster (long and boring story - getting an award for our work on OPUS). Anyway, just before I left, I asked him about my previous Crashing Cars problem. He wasn't by any means the first PhD I'd asked about this, and I'd even asked a few physicists. I was hoping of course, that he would immediately say I was being stupid and had missed something obvious, but he found the problem as bothersome as I did.

I continued to mull it over a bit, and even found the problem had some more unsettling properties to do with the masses of the car, but didn't make any progress unraveling the mystery. Well, a few days later Brian CC'd me on an email to someone with whom he had clearly been discussing the problem with a possible solution. Having read it a good few times and thought it over it makes sense to me and it doesn't come as a surprise that Brian was the one who cracked the central nub of the problem. I'm a lot more cheerful about it now, but it goes to show that dark nasties can lurk in surprisingly simple problems.

I was brooding some more about the frames of reference thing and maybe beginning to see where the paradox lies. Thing is [perhaps] that the observer in the car is non-accelerated only up to the moment of impact: we can't use him to assess KE after that moment with the same cavalier abandon that prevailed beforehand. [Especially since he'll have a headache.] Thus it is not legitimate to say: "from car 1's POV, KE before = 2mv2, KE after = 0 + 0, therefore KE dissipated into crunch = 2mv2". Which would be very troubling since it would appear to let us distinguish between states of rest/uniform motion by Physics.

What we can say instead is that from the point of view of a non-accelerated observer *travelling initially with car 1*, the KE before = 2mv2 and the KE after = 1/2 2m (-v)2 = mv2 so the KE going into the impact process = 2mv2 - mv2 = mv2. Which agrees with the observer on the roadside! So maybe the old geezer with the mop of white hair and the century's most iconic formula was right after all. I'm sufficiently encouraged to copy this email to my tormentor in Jordanstown and see if it allays his apprehensions. Hi Colin!

Debian is my favourite distribution of GNU/Linux. It's a well respected and well known brand, although I was almost stunned while on business in London last Friday to meet someone who knew about Suse, and Red Hat but wasn't even aware of the existence of Debian. I like Debian's astonishing infrastructure, and its community led approach. It has been on the verge of releasing its next stable version, Lenny, for some time. I've been waiting for that freeze to end to have my debian packages of OPUS uploaded, since there is currently no real rush and I wanted to do more "upstream" work on them. At that point I wanted to start the long path to DD status (via maintainer).

Noodles, who is a DD, has recently commented on his frustration that Debian procrastinates at the end of every release cycle. This seems to be true, and internecine war always seems to erupt over issues that should have been solved long before (or alternatively after) the release. I'm also sympathetic to his suggestion that Debian's voting procedures could be improved.

Reading through Planet Debian today, I am more depressed than ever. Debian's secretary has resigned over voting issues and the vitriol unleashed by them. I'm not making any comment on that. There is already a constitutional pathway for an interim secretary, but now, the project can begin to rip new wounds in itself over the resignation, rumours of expulsion procedures and what to do next. What to do next is damn important, but so is the release.

I was in Plymouth in September with Lenny installer beta 2 CDs with Lenny images that wouldn't even install on the new hardware in a problem frustrating similar to one I found months before (Ubuntu, derived from Debian, embarrassingly did so without problems). I dare say that issue has been fixed (I can no longer test it), but it's a horrible reminder of how a prolonged freeze can lead to an OS that can be born obsolete in the sense that it can't install on newer hardware.

Ok. I dislike the X-Factor. I think Ben Elton's book Chart Throb pretty much says it all.

I managed to watch very little of it this year (harder than it sounds given the exposure you get from other people) but did manage to be totally oblivious to the outcome. I remain so, with pride. However, I did hear that the song they are torturing this year to get the Christmas Number 1 is another cover of Leonard Cohen's Hallelujah.

Well, I suspected that the facebook group was right on the matter, that it would be a soulless piece of merchandising, I just heard it, it is. Standard over produced tosh.

Well, I whole heartedly agree, Jeff Buckley's version is not only better, it is one of the most beautiful performances of any song I have ever heard and has long been a favourite of mine. I already own two copies of it on genuine real physical media, but I'll be downloading too. Probably futile, but I'll feel better for having tried. If you want to join the rebellion the link above has the details.

Oh, and you kids, get off my lawn!

Consider two identical cars, each travelling at a constant velocity v towards each other. Suppose that they crash, and to simplify things, let's not consider any rebound. Then the energy of each is kinetic in nature and so the energy of the crash is given by



Ok. That's a nice way to show the energy of the collision goes up with the square of velocity. Now, according to the principle of relativity this should be an identical situation if you consider it from the reference frame of one of the cars. In that case, the car you are looking at has a velocity of 0, while the other car has a velocity of 2v. Now the total energy of the crash looks like



So. Why the discrepancy?

I use Icedove for mail mainly (the Debian variant of Thunderbird - a long and not very interesting story). I generally like it. I've used pine and mutt, but generally get too much stuff to view to make a text mode editor much fun. I've used evolution, but it was for a long time very slow, so now I tend to use Icedove. It locks up rather frequently on imladris (my main machine) running Debian unstable, and while I've now downloaded some debugging symbols I haven't devoted the time to finding out why yet.

Anyway, there are three things about it that really, really peeve me:

• Why don't the damn tags in version 2+ actually stick (in my imap folders, in dovecot) so that I reliably see them using the same flaming program in work?
• The feature to show a newly received mail is great, but it would be one thousand times more useful if I could tell the program to only feature mail in certain folders and/or not others. I don't really need to be told about how many thousands of new messages I have in my spam filtering folders all the time.
• Why does the exact same program view emails on my laptop in such a way that I frequently see all the "Your editor does not support graphical content" stuff on such emails?

Yes, I've tried google, yes, I've tried FAQs. Can't find the answers. I'm sure I've looked right past them. Anybody?

BTW... Two posts in one day? Not an excess of free time, trying desperately to take my mind of one of my cats who is very ill atm.

On Saturday night, quite by accident, I sat down to watch "Einstein and Eddington" on the BBC. Einstein has been an inspiration to me from an early age, and I'd known a lot about his life and work, and for many years a picture of him has adorned my room or office, though not at the moment as it happens. I suppose in compensation einstein is the hostname of my work computer at the moment.

Anyway I was also for this reason aware of Arthur Eddington, and his famous experiment to verify that gravity bent starlight. I was also aware of his famous quote regarding being one of three men who understood General Relativity. Nevertheless, it was fascinating to see the historical context of the interaction between these men, and a bit more of Eddington's life. I would recommend the programme highly, so if you're in the UK you have a few more days to catch it on iPlayer.

Great performances from Tennant and Serkis.

I was just reading the BBC's article about the leaked details of BNP members.. It's an interesting story, although of course here in Northern Ireland we have our own unique brand of prejudiced politics. (This reminds me of Frankie Boyle joking about Al Qaeda trying to bring religious intolerance to Scotland, that they were centuries behind the competition and didn't even have their own football team. That and they were dealing with the kinds of people who punch burning men in the face.)

Anyway, I'm digressing. At the bottom of the page there was the usual comment form, but I think the disclaimers above and below the form bear some reading. Is this a trap for particularly mentally slow BNP members (yes, I know you're all making your own punch line now).

Update I did of course contact the BBC about this rather than just laugh about it here, and as is often the case, they fixed the problem with the usual efficiency.

Today I was asked to look at a computer that was claiming to be infested by viruses following clicking on a link from facebook. This was of course a Windows situation, so I was unsure how much help I could be given how long it's been since I had to use Windows.

Anyway, I booted up the computer which swapped incessantly due to the low memory it had, but also due to whatever malware was at play. So eventually windows booted up, launched Internet Explorer which was already suspicious, and the systray showed a flashing shield. It didn't take me too long to work out that the window full of virus reports was bogus. Eventually I killed all the running crap in the task manager (ctrl-alt-del) then loading the task manager to start closing various applications. I also closed the "WAV" and suspicious "cmd" processes that were taking much of the CPU and had no good reason to be running.

After that, I nuked the contents of "C:\Program Files\WAV" suspecting that to be the problem, and for good measure ran the registry editor (Start, Run, type regedit and hit enter) and searched for occurrences of WAV that pertained to this stuff and nuked them. That is, of course, not for the unwary. When I restarted all was well and the problem was gone. Well, I removed the shortcut on the desktop for the now non-existant WAV. I'm putting this here so it can be forwarded to a few other victims.

Friends shouldn't let friends run Windows. I know...