At your exact age, Pierre Curie died in an accident. He was a physicist who won a Nobel Prize with his wife Marie Curie for discoveries in radioactivity.
Monthly Archives: April 2009
Some Things About Science
Dot Physics: Some things about science
Aristotle and the other Greeks: They started with assumed truths like heavy things fall faster than lighter things. From that they deduced ideas about motion. The problem here is that if your “assumed truths” are wrong, you are in big trouble. They did not actually test their assumed truths. If they did, they wouldn’t be assumed.
This is a common bugbear of the crackpot, too, who starts with some flawed assumption about how nature behaves and ends up concluding that his perpetual motion machine will work.
Two For One
One of the things we’re investigating is pulsed laser systems, because they’re fun, but (especially for funding purposes) also because they are the basis of optical frequency combs (as I’ve mentioned). And things are pulsing along. One of the things that was noticed was that light from the pulsed system, running at 1560 nm, was showing up on a Silicon CCD camera. The Silicon response peaks at 900 nm and drops pretty sharply, petering out at 1100-1200 nm. There’s no way it should respond to a 1560 nm photon.
And it isn’t. It’s responding to pairs of 1560 nm photons. This is a pulsed system, so you have high peak power making it a lot easier to see nonlinear responses like two-photon transitions, because they scale as the square of the intensity. (more photons incident per unit time means a better chance to have two interacting at once, Having n photons means that if you look at any photon, the chance of another photon being around is n(n-1)) Two photons have enough energy for the interaction, since that’s the same as having a 780 nm photon, which is well above the “to be detected you must be this tall” energy cutoff
Here are two images. The square is a beamsplitter cube, and the white blob is the light. The top image is the pulsed laser, and the bottom one is a CW beam, both with around 10 mW average power.
The pulsed laser is saturating the heck out of the CCD, so the spot is really a lot brighter than from the CW beam, though we can’t say for sure based on this quick look. Even though the average power is about the same, though, the pulsed laser is repeating at about 10 MHz, and the pulses are less than a picosecond, so all of the light is being delivered in less than 10-5 of the time, so the peaks have powers measure in kW.
Worthless? Bah!
physics and physicists: “I’ll Never Use The Skills I Learned In Physics”
zapperz attacks this in a couple of ways, such as the idea that you (can) learn critical thinking skills
The “skills” that one learn out of a physics/science course goes BEYOND physics. It is a skill of thinking things through and systematically. It is the skill in knowing what KIND of evidence is required for something to be considered to be VALID. This is highly important no matter what you do. How do you know that something somebody utters on TV is valid? Most of the time, people are persuaded not based on valid evidence, but based on personality of the presenter and all the bells and whistles. Apply this to the world of politics, where phrases fly off into the air as if they are facts, or as if simply by saying it, it is true. The same can be said with regards to the battle between evolution and creationism. The inability of some members of the public to actually think through something THIS obvious clearly shows that the skill of analytical thinking isn’t there!
That and the other points are certainly important, but I’ll go a step or two lower and look at some actual physics applications. I don’t know precisely what is taught in Physics 140: How Things Work, but I’d guess a few basics involved would let you figure out that the truth about turning the heat down during the day if nobody’s home. “Conventional wisdom” says that it takes more energy to heat the house back up, but the actual physics confirms the conventional wisdom to be wrong. Or a simple analysis to verify that buying a long-life CFL will save you money over incandescent bulbs once you figure out actual energy use, despite the cost-per-bulb being higher. E = Pt is simple physics, but physics nonetheless.
A word of advice for Ms. McMillan: if someone asks you to invest in a device that creates energy, for which you will be able to charge money and make a profit, it may appear to be a sound investment from a financial perspective. But the physics you so casually dismiss guarantees that it is not.
(on a personal note, I’ve found that most of basic finance is pretty easy if you can do physics. Problems in financial literacy and science literacy do share a common problem: math literacy)
What it is
Fun fact: the nerves in your skin don’t actually sense temperature; rather, they sense the flow of thermal energy. Metals below body temperature generally feel cold to the touch because they are very effective at conducting away thermal energy. Plastics at the same temperature feel warmer because they are much worse thermal conductors.
Roll Your Own
What’s next — self-assembling snowmen?
Smitty! Safen Up!
Not only was Wednesday Tax Day, it’s also audit season at work. I got a call recently about one of my recurring purchases for nitrogen gas (and the bottle rental), to make sure it’s within the rules. You see, I’m not allowed to buy hazardous materials for the lab with my credit card, with the exception of “commonly available HAZMAT,” which I interpret as anything I can get at the hardware or drug store. Examples of these would be batteries and toner cartridges (two things explicitly listed in the government instruction), partly (mostly?) because they have disposal restrictions.
There was a brief period where the rule was being interpreted as no purchases at all unless you were HAZMAT trained, but we had nobody with a credit card who had such training. There were people who could buy Certaindeath Juice™ if need be, but only if the order had enough zeroes on it — you needed to buy Certaindeath Juice™ in bulk — and our orders didn’t qualify. So I couldn’t buy things that a nine-year-old with a five-dollar bill could get at the grocery store. That Catch-22 eventually got cleared up, but not because anyone understood the phrase “mutually exclusive” or could read a Venn diagram.
So, back to the nitrogen. Is it a hazardous material? I don’t really know for sure. There are HAZMAT rules for sale, use and transport, and I don’t know which ones apply to my situation. You can’t (easily) ship compressed canisters on an airplane — I’ve purchased some things which had to be shipped by ground transport because of this restriction, but once you took care of this, there were no HAZMAT issues. So for nitrogen my gut says no, and more importantly, my lungs say no, based on continual exposure to an 80% mixture for an extended period of time, interrupted briefly by replacement with Helium on a few occasions. I can’t find any official wording that tells me which criteria I should use for HAZMAT purchase restrictions and how to differentiate it from a non-hazardous material, in such a way that you don’t just classify everything as hazardous. That would be the government way, of course. Nitrogen is a simple asphyxiant — it can displace oxygen and you can die. But I can have the same outcome with the plastic bag, so I fear that somebody is going to insist that plastic bags be deemed HAZMAT. Filing cabinets can be made top-heavy and become a danger if they were to fall over and crush you. (Back in my navy days we got periodic safety messages that invariably included a story of someone tipping a vending machine and being crushed. Also the tally of how many things fell off of aircraft). Paper? I can cut myself and bleed to death, or wad it up and choke on it. Is paper HAZMAT? Oh, crud. I hope I don’t give anyone ideas.
The criterion can’t be that there is an MSDS for it, because you can find an MSDS for water. I can’t buy drinking water because of food purchase restrictions, but what if I needed some deionized water for the lab? What are the actual dangers? Hmmm. Prolonged exposure will make you pruny just doesn’t seem to cut it for a hazard. Drinking gallons of the stuff can kill you, but as with the above, examples, that just means that everything is hazardous. At least I have the “commonly available” loophole.
Seems to me that a common-sense approach says no. It doesn’t react with me chemically, it’s not toxic and isn’t a fire hazard. There are safety issues, as with all things; if you try hard enough, anything can be dangerous.
The Truth Hurts
The Onion: Roster-Depleted Bears Sign Tire Swing For Cutler To Throw To
Analysts say that, while the move is somewhat unorthodox, Chicago was prudent in passing on veteran free agents Amani Toomer and Joe Jurevicius in favor of offering the tire swing a 3-year, $2.4 million contract.
I have Cutler on my Fantasy team, and he led me to our league’s Super Bowl (which I ended up losing in a stunning week-17 scoring collapse, while my opponent exploded for 97 points to overcome my 26-point lead from week 16 and win by 31). The trade to the Bears was a definite downgrade for me.
R1D1
In New York, we are very occupied with getting from one place to another. I wondered: could a human-like object traverse sidewalks and streets along with us, and in so doing, create a narrative about our relationship to space and our willingness to interact with what we find in it? More importantly, how could our actions be seen within a larger context of human connection that emerges from the complexity of the city itself? To answer these questions, I built robots.
Tweenbots are human-dependent robots that navigate the city with the help of pedestrians they encounter. Rolling at a constant speed, in a straight line, Tweenbots have a destination displayed on a flag, and rely on people they meet to read this flag and to aim them in the right direction to reach their goal.
Schneier notes
It’s a measure of our restored sanity that no one called the TSA. Or maybe it’s just that no one has tried this in Boston yet.
Maybe We'll Do In a Squirrel or Two …
… hundred.
Spokane parks to detonate squirrels
The parks department says the Rodenator is a humane way to kill the squirrels. But it warns area residents that the explosions sound like gun shots, and to not to alarmed by them all week.
The Rodenator Pro pumps propane and oxygen into the tunnels of squirrels, then sends an electric spark that causes an explosion. The shock waves kill the squirrels and collapse their tunnels – but in a humane way, the agency said.
The agency spokesman sounds a lot like Carl Spangler.