TV isn’t real, especially when it comes to science. PhD comics gives an independent confirmation.
Monthly Archives: April 2009
Science = Imagination
Bad Astronomy: Science IS imagination
People don’t understand science.
And I don’t mean that your average person doesn’t understand how relativity works, or quantum mechanics, or biochemistry. Like any advanced study, it’s hard to understand them, and it takes a lifetime of work to become familiar with them.
No, what I mean is that people don’t understand the process of science. How a scientist goes from a list of observations and perhaps a handful of equations to understanding. To knowing.
Redoubtable
The Big Picture: Alaska’s Mount Redoubt
Beginning March 22nd, 2009, Alaska’s Mount Redoubt, began a series of volcanic eruptions, and continues to be active to this date. Ash clouds produced by Redoubt have pushed 65,000 feet into the sky, disrupting air traffic, drifting across Cook Inlet, and depositing layers of gritty ash on populated areas of the Kenai Peninsula and Anchorage, about 180 km (110 miles) to the northeast. Mount Redoubt has erupted at least five times since 1900, with the most recent event taking place in 1989. (27 photos total)
This is Not a Random Post
Or is it?
Humans are not very good at generating random sequences; when asked to come up with a “random” sequence of coin flips from their heads, they inevitably include too few long strings of the same outcome. In other words, they think that randomness looks a lot more uniform and structureless than it really does. The flip side is that, when things really are random, they see patterns that aren’t really there.
Come Again?
I can try now, even though it’s not working? Gee, thanks.
Come visit any time we aren’t at home.
It's a Setup
When I taught I tried to instill the concept that you should be able to pass an exam without a single correct numerical answer, because the problem set-up was the most important part of the solution. Few of my students believed me, but I see that my experience was not unique. The First Excited State has Missing the Important Stuff, which sets up a response at Uncertain Principles, The Process Is as Important as the Answer
Chad points to the problem of giving a problem with only algebraic expressions
The problem with this method, of course, is that students hate it with the burning passion of a million white-hot suns. If you think they get unhappy when they don’t have the exact numerical answers to work toward, just wait until you see their reaction to no numbers at all.
Physics Malpractice
Via physics and physicists I see a story about how golf can be hazardous to your hearing. And the story botches the physics. (I don’t know if it’s the journalist or from the original journal article)
The coefficient of restitution (Cor) of a golf club is a measure of the efficiency of energy transfer between the golf club head and the golf ball. The upper Cor limit for a golf club in competition is 0.83, which means that a golf club head striking a golf ball at 100km per hour will cause the ball to travel at 83km/h.
Well, that’s just wrong. The Cor tells you about the kinetic energy, so it won’t be the same for the speed, because KE depends on v2. i.e. if a ball is dropped from 1 meter and bounces, returning to 0.83m, the impact speed is ~4.4 m/s and the return speed is ~4.0 m/s, which is 0.91 of the speed.
Another problem is that the mass of the clubhead is not the same as the mass of the ball. Even if the Cor applied to speed, the statement is incorrect. In the limiting case of Cor=1 and the ball’s mass being negligible, the ball would leave at twice the clubhead speed.
The actual equation is v = u*(1+e)/(1+m/M)
v is the ball’s speed, u is the clubhead speed, e is the Cor, m is the ball’s mass and M is the clubhead mass. (This is trivially derived using conservation of momentum and balancing the kinetic energy equation to account for the loss) Using e = 0.83, and assiming the M=4m, we see that v = 1.46u
Update — This is using a definition of Cor on terms of energy. I couldn’t find how the USGA was defining it when I was composing the post, but further research (and noted in the comments) indicates that it is indeed the fraction of the speed retained after the collision. That changes the details of the analysis, but the article’s numbers are still wrong — the ball’s speed is larger than the clubhead speed. I still haven’t found a mathematical definition of how the USGA applies this to a golf club
That makes e in the equation the square of the Cor (so e = 0.689), which means that the ball leaves the clubhead at v = 1.35u
Rolling, Rolling, Rolling
A few days ago I was relating the cans-in-a-blanket problem, and retelling the vacuum joke and story to someone who had not yet heard them. One of my colleagues commented on a problem he had been given during an interview, also involving cans of soda:
You have two cans, one filled with ice and the other with liquid, but otherwise identical. The cans are rolled down an incline. Which one reaches the bottom first?
Much like the previous problem, I think there is a common misconception at play here for some people who get the answer wrong, and I’ll get to the explanation below. One of the people in the conversation said his first impulse was the wrong answer, but when we discussed the physics, we all agreed on the solution.
I set up to do a demonstration, though my first attempt was thwarted — I filled up a can with water and popped it in the freezer, hoping the can would be strong enough to hold together and have the ice expand vertically. It wasn’t.
I think the problem being that since ice will freeze from the top down and outside-in, the ice adhered to the can too well to let it expand upward as much as I hoped. (BTW — Black Cherry Citrus? Blecch. I bought it by accident when they redesigned their color scheme and introduced the flavor)
So I did it again, adding a little bit of water and letting that freeze, repeating the process several times until it was full, and it worked. Here is the experiment to investigate the problem given above:
For those who think that the liquid-filled can will roll more slowly, I think I know what the misconception is: most of us have seen or done the experiment with spinning an egg, and a hard-boiled egg spins readily while the unboiled egg doesn’t. So the intuition is that since liquids don’t spin readily, the liquid-filled can won’t want to roll very fast. And, as we can see, that’s wrong.
The reason the intuition is wrong is from a misinterpretation of the reason the unboiled egg doesn’t spin — it’s because it’s difficult to transfer energy and angular momentum to the liquid by spinning the container; the coupling between them is weak. And angular momentum tells you the tendency for something to spin — it only changes when you apply a torque. With the soda cans it means that the work being done, adding energy (gravity acts on it, and there is a torque from the friction of the treadmill causing rotation)but this energy isn’t being added to the liquid, so it must be going into the can itself, which isn’t very massive — almost all of the energy goes into translational kinetic energy. The frozen water, though, does rotate with the can, so the gravitational potential energy has to be shared between translation and rotation of the can + ice system, so the translational kinetic energy (and therefore speed) is smaller.
The Place to Be
Success!
The rough headcount for the Open House was about 9,000 visitors. This was the first one I had worked (there hadn’t been one of these since 2001) and the expectation from the earlier events was that we could get “a few thousand” people, so I’d have to say that we exceeded expectations. The weather was absolutely gorgeous for early April — mid 60s and literally no clouds. There was some wind early in the afternoon, but even that minor annoyance died down.
We got a lot of traffic at the geocaching table. A fellow geocacher helped out (and a few others came to visit and nab the “puzzle” geocache located at the Observatory); we chatted with people and explained the activity to the adults. For the kids, it was more interactive — I handed them a GPS receiver and walked them through the cache finds: a fake rock and a film container, with log books in them. The areas open to the public weren’t conducive to larger caches, and there was no budget for trade items (or give-aways, in this case). But with the response we got from this event, maybe there will be an opportunity for a more elaborate activity next year.
I didn’t get a chance to check out the other presentations (though I had seen several of the posters; a network issue prevented several people from “seeing” our plotter, so they sent me files and had me print them) I know the lines were long for the “big” telescopes, and there were more than a dozen amateur astronomers who set up scopes (some more than one) for viewing. The sun (sans spots) during the day, and then whatever was up at night. I arrived at 1 for some setup work and left around 9, which is when they were going to close the gates, and there was still a considerable line of people waiting to get in. Not sure if they stayed open later than the planned 10 PM. It would have been disappointing to close down before everyone got a chance to look through a few telescopes, but security makes the call on things like that.
The best part about all of this was the kids. You could tell that some had been dragged there, but for the most part they were very engaged and enthusiastic. The ones who did the geocache finds were, and I heard some very positive, spontaneous comments from them in the area where the telescopes were set up. When I was returning some GPS receivers to Geoff, the PAO, the youngster stepping down from the telescope shouted out a very sincere, “I saw the MOON!” That’s worth the price of admission right there.
Here’s the view of the lawn where the small telescopes were set up.
Things got busier as it got dark, but flash photography tends to annoy people who want their eyes to be dark-adjusted, so I don’t have any pictures.
Wonder Woman's Other Mode of Transportation
Spectacular and See-Through: Dude, Where’s My Canoe?
I have a sudden urge to take up scuba diving.