Cycle Quark

I went to see the new Pixar movie, WALL-E, last night. I throughly enjoyed it. The villan of the movie was a corporation, Buy N Large, which makes Walmart look like a boutique shop. It is abbrievated all throughout the movie as BNL. I hope my friends from Brookhaven National Laboratory (BNL) don’t take it personally.

XKCD got written up in the NY Times. I discovered from the article that the author is a physics major. I knew he had to be a geek, but physics is as good as it gets.

Normally I would not mention xkcd again since my last post is about it. However, the Large Hadron Collider gets mentioned on xkcd, so I had to link to it. If he mentioned blackholes, it would have been really topical.

Mythbusters, Zombie Feynman and a meditation on the meaning of science. What more can you ask for?

Mahalo Daily is a short video podcast hosted by Veronica Belmont that covers a different topic everyday. One day it is hangover cures and another it is the perfect grilled cheese sandwich. Well I checked on the recent ones today and I saw that there was a podcast about SLAC. It is not as good as a real visit, but you should check it out anyway.

There is a nice article in the New York Times on the requested science funding in the President’s recently submitted budget. It discusses both the relatively high levels of funding requested and the difficultly that recent similar requests have had getting through Congress.

“Across the campus trees broke out in absurd petaled profusion. Life returned to life, sporting a spin, strangeness, and charm that Spiegel had never suspected.”

Richard Powers, Plowing the Dark

Richard Powers writes literary fiction. He tackles hard subjects and his writing is dense with allusions. He frequently writes about the intersection of art and science, which is definitely true of this book. A physicist would recognize the spin, strangeness, and charm int he quote are quantum numbers of elementary particles. I wonder how readers will pick that up. What does that sentence convey to non-physicists.

Joel Achenbach’s Sunday Washington Post Magazine column discusses his visit to Fermilab and how much he learned. I felt compelled to post two comments, including one on an attempt to build a cloud chamber at CERN.

The mention of the cloud chamber required me to tell this story. I did my Ph.D research at CERN in Geneva, Switzerland. We used a bubble chamber which is much the same idea as a cloud chamber but used cryogenic liquids instead of humid air. There were only a small number of American graduate students at CERN in those days, and we tended to hang out together when we weren’t working. One day we decided to build a cloud chamber. One of the key components of a cloud chamber is dry ice. Well, it turns out that modern particle physics labs do not stock dry ice. You can get liquid nitrogen by the ton or liquid helium, but no dry ice. We took a bus all the way across Geneva to find dry ice. The cloud chamber worked and we saw particles in real time.

Helping my daughter with her high school physics homework is a much different activity than lecturing to 200 students. I had a real insight last night into the kind of mistakes that students make. The problem was a classic block on a turntable problem. The turntable accelerates at a constant rate and the question is how long before the block slides off.

In this problem the mass of the block was not given, and that was a real stumbling block for my daughter. I told her to just write down m for the mass and keep working. Later in the same problem she needed the angular velocity and was given the angular acceleration. I said just find the angular velocity using the acceleration. I assumed that she would write

ω = αt

but she said that she did not know the time. I pointed out that she was looking for the time. I got very excited at this point. I had discovered a fundamental problem she was having. Her bad habit of plugging in numbers immediately actually prevented her from doing this problem. I probably got too excited. She started to cry.

Since the beginning of the year I have encouraged her to solve the problem symbolically as far as possible and substitute in numbers as late as possible. In general she has ignored my well thought out fatherly advice and tried to plug in numbers as soon as possible. After she calmed down I explained how her way of doing things prevented her from solving the problem. I hope this lesson sticks.

My youngest daughter is taking algebra based physics in high school. The middle one is taking AP calculus in high school, and the oldest is taking honors calculus-based physics. They are keeping me busy.

My youngest was asking me about conservation of momentum problems last night. The book did something that I liked. It did not ask for actual numerical answers, but instead asked if the available information was enough to solve the problem. For example, you know the masses and momenum of two objects before a collision and the velocity of one after the collision. Can you find the velocity of the other after the collision. After doing a few of these I instructed her to write the equation for conservation of momentum.

m₁v_1i + m₂v_2i= m₁v_1f + m₂v_2f

Now cross out each item that you know and ask if there is only one unkown left. I get to cross out both terms on the left side since I know the initial momenta and I can cross out m_1,m_2, and v_1f. I am left with just v_2f so I can solve for it.Well it turns out that writing that equation which is just second nature to me is a big stumbling block for a new student. I immediately switch to abstract thinking. There is a lot of content in my choices of labels. 1 and 2 indicate that there are two different mass objects and they can have different velocities. The i and f indicate that the velocity can change in the collision. The fact that there is no i and f on the masses means that objects do not stick to gether or fall apart.How does one encourage that conceptual leap? Do you do many concrete examples and hope the student begins to infer the abstraction or do you lead them through it?

Update: I think some experimental introduction is probably the best approach. Measure a bunch of momenta before and after a collision and see that the momentum is always conserved.