barnabas_truman: (young whistler)
Today I met a bunch of new (to me) students and talked with them for most of an hour about temperature and heat flow and conservation of energy and graphs and equations. Afterwards three of them independently came up to me to tell me that my teaching style is "outstanding." I'd call that a successful first day of class.

Later, in office hours, a familiar-looking student came in for some help with the same subject matter, and to get my advice and opinions in general on physics classes, learning about logic, a possible philosophy minor, and how to apply all of this towards an eventual career in emergency medicine.

He then told me that three years ago he was in the summer orientation algebra review class I taught, and apparently what I wrote on his final exam had had a huge impact on him. It seems he hadn't really applied himself much during the summer orientation program, and during the final he felt totally lost and wrote a rather emotional note to me on the back apologizing to me, the instructor, for doing so badly. He tells me I wrote a very long and thoughtful response (I just barely remember this myself) telling him that he doesn't need to apologize to me; that the only person harmed or helped by his studying habits is himself; and that it's going to be okay--that a big part of the reason for this summer program is to give him a chance to make mistakes and learn from them in a safe space without huge negative consequences. I didn't fully realize it at the time, but apparently this was exactly what he needed to hear.

It's always nice to find out, even years later, that what I've done has made the world a little better for somebody.
barnabas_truman: (oldstyle)
This evening I went to the awards ceremony that concludes a summer orientation program that my department offers for incoming first-year students. I was primarily there to give out balsa wood gliders as trophies to the teams that had scored the most points in a Physics of Paper Airplanes workshop a few weeks ago... but after doing so, I realized that I had a moment in the spotlight with a captive audience of over 200 cheerful students who already think I'm pretty cool. I launched into an impromptu speech (because it turns out that what I'm really best at is making stuff up on the spot) about science, technology, and social responsibility. I'm going to try to type up as much of it as I can remember while it's still fresh in my mind...


I'm a firm believer in the idea of salvation through technology; salvation through knowledge; the notion that we can make our lives and our world better by understanding the universe and finding ways to manipulate it.

It is amazing how powerful technology is in the modern world. We can communicate with people all over the globe instantly. We can travel to the other side of the continent in mere hours. We can survive injuries and illnesses that, a century ago, would have been assumed invariably fatal. We can produce enough food by having 1% of our population working on farms instead of 90%. Amazing advances.

But technology comes with dangers as well. We can kill each other with a twitch of a finger. We can destroy entire cities in the blink of an eye. We can poison our own air without even trying.

We need the technology, but we also need to learn how to use it responsibly, and how NOT to use it. The advances in what we CAN do must be paired with careful thought about what we SHOULD do.

So by the power vested in me by nobody in particular, here is what I wish for all of you, whether you're going into the sciences or not:
the perception to learn about the world around you,
the cleverness to design amazing new things,
and the wisdom to use them to make the world a better place for everyone.

And if you EVER need any help in ANY math or science class... you know where to find us.


That's it as near as I can remember. It seemed to go over remarkably well with the students. (And no, I didn't actually say "With great power comes great responsibility," but I was thinking it pretty hard.)

See, I've been thinking a lot recently about my own responsibilities as a physics teacher who strongly believes in peace and social justice. I've known for years that it is my responsibility to teach physics to all who request it... but I also feel a need to be a paragon of pacifism. I have often worried "what if I teach physics to some students and then they use what I've taught them to design weapons?" Now I realize what I must do: pair my direct teaching of physics with some subtler teaching of ethics, using my mythic reputation as leverage. Good to know.
barnabas_truman: (oldstyle)
Summer session: ten weeks' worth of physics material packed into only five. Every support workshop is a rush; every day I find that students are studying material about a week ahead of what I would expect. So often in the past few weeks I've been reminded of Feynman's footnote:

"How I'm rushing through this! How much each sentence in this brief story contains. 'The stars are made of the same atoms as the earth.' I usually pick one small topic like this to give a lecture on."

So much marvel and wonder in the universe; so little time to discuss it in detail. Such is life.
barnabas_truman: (math)
(cross-posted from Storytelling Physics)

This evening I spent nearly 2.5 hours running the final review session for the differential equations students (their final is tomorrow morning). There were 46 students there! They ran out of chairs, so they sat on the floor; they ran out of floor, so they stood in the hallway. I gave them general tips on test-taking, I gave them specific tips on this particular professor’s tests, and I walked them through long and complicated problems on weighted strings, vibrating membranes, eigenvectors, and quantum oscillators. I told them that no matter what happens tomorrow, they’ve survived a full quarter of the toughest lower-division math class that this university offers, and that no matter what classes in math or physics or engineering they take from now on they’re always welcome to come to my office hours for help. When we finally called it quits so I could catch the bus I got a hearty round of applause and a bunch of handshakes. Good times and a satisfying end to the quarter.
barnabas_truman: (army)
Santa's not *from* the North Pole, but he does use the North Pole as a starting point for his annual journey. From his secret base in Lapland, he flies to the Pole, where the circuitry in his sled interacts with the unique polar magnetic field to create a quantum multiplicity. Infinitely many virtual Santas then fly south along infinitely many possible paths, bringing presents to every household, and finally converging at the South Pole and merging into one Santa again. This is also why children need to go to sleep before midnight on Christmas Eve; the whole quantum multiplicity effect relies heavily on being unobserved!

Trust me; I'm a physics teacher. We know how these things work.
barnabas_truman: (army)
"So the plurals would be Centigrades, Celsiides, and Fahrenheiten."

"What's the plural of Rankine? Rankeen?"

"No, Rankine is already plural. The singular is Rancow."
barnabas_truman: (kimiko)
(We've been running the air conditioner upstairs, but not downstairs.)

*going downstairs*

"Wow, it's hot down here!"

"Interesting. Perhaps temperature is inversely proportional to elevation."


"As you yourself observed, we went downstairs and it got warmer."

"How on earth would that work?"

"Conservation of energy, of course. We decrease our elevation and thus lose potential energy, so thermal energy increases as a result."


"Trust me; I'm a physics teacher. I know how these things work."
barnabas_truman: (young whistler)
Notes for a reference sheet I'll be making for my physics students later this summer:

-20°C: inside a freezer
0°C: water freezes/ice melts
4°C: inside a refrigerator
10°C: winter in Davis
20°C: comfortable and a bit cool
25°C: comfortable and a bit warm
30°C: time to hit the pool

37°C: inside your mouth
40°C: summer in Davis
50°C: a very hot day in Death Valley
100°C: water boils/steam condenses

175°C: baking cookies
205°C: baking frozen pizza
barnabas_truman: (young whistler)
Note to self: get some of this beaded chain from a hardware store.
barnabas_truman: (young whistler)
I got quite a workout this morning helping my brother put a roof on his new yurt. Hoist hula hoop-sized wooden center ring to top of scaffold, lift forty 15-foot long wooden support beams into place between wall and ring, dismantle and remove scaffold, realize that all beams are upside-down, rotate all beams in place, aaaaaand break for lunch. Good times.

Also it occurred to me that the framework of the yurt would make an excellent statics problem for a basic physics class--analyze all the forces acting on the beams, the cable they're nested on, and the central ring.
barnabas_truman: (oldstyle)
Long ago I stood on the balcony of a physics lecture hall, watched the leaves of a nearby tree shiver in the wind, and pondered the physics of their chaotic dance. Today I passed by the same building, watched the leaves dancing again, and thought:

Twelve generations of leaves have grown and fallen since I last paid them any mind, but the tree remains and each new leaf can still dance.

Twelve generations of students have passed through this hall since I learned physics in it, but the building remains and the class is still taught.

Twelve years of experience have shaped me since I first watched this tree, but I remain myself and I still think these thoughts.

These moments of clarity--these deep connections that grow between my memories, the land's memories, my future, and the land's future--are among the best things about returning to teach in the place where I once learned. Would that everyone had such opportunities.


Mar. 15th, 2013 11:26 pm
barnabas_truman: (math)
(referring to this gravity simulator)

Try placing a positive and negative mass object next to each other. They wind up propelling each other in the direction of the positive mass.

I thought about this for a bit and realized WHY they do this.

Suppose there are two positive masses, M1 and M2.

Gravitational force is Fg = -G·M1·M2 / r2,

and F = m · a, so a = F / m,

so the acceleration on, say, M1 should be
a = Fg / M1 = -G·M2 / r2.
The negative signifies that it's accelerating towards the other mass (i.e. working to decrease the distance).

Now suppose we're dealing with two negative masses, -M1 and -M2.

Now the gravitational force is Fg = -G·(-M1)·(-M2) / r2 = -G·M1·M2 / r2,
which is the same force as before, because the two negatives cancel out.

But the acceleration on -M1 is
a = Fg / (-M1) = G·M2 / r2.
That's a positive acceleration, so the two negative masses repel each other!
(Interesting side-note: a negative mass would accelerate in the opposite direction from the applied force.)

Third case: opposite masses, M1 and -M2.

This time the gravitational force is Fg = -G·(M1)·(-M2) / r2 = G·M1·M2 / r2,
which, unlike the other two cases, is a positive force.

Now the acceleration on the positive mass M1 will be
a = Fg / M1 = G·M2 / r2.
That's a positive force, so the positive mass is repelled by the negative mass.

But the acceleration on the negative mass -M2 is
a = Fg / -M2 = -G·M1 / r2.
A negative force means the negative mass is attracted to the positive mass.

That's why the end up chasing each other!

For extra fun, generate a proto disk and plop a -OMG into it somewhere off-center.
barnabas_truman: (army)
Today in my physics workshop I taught about some water flow stuff, some electrical flow stuff, a lot of heat flow stuff, and an introduction to an equation that ties all of them together. I love covering topics like this because much of it is new ideas that the students are seeing for the first time, yet can be related directly to their everyday experiences.

In particular, I was discussing the idea of thermal conductivity--a measurement of how easily heat can pass through a material. "When would you want low conductivity?" I ask the class; "what's a situation where you want heat to flow very slowly?"

Silence. Somebody ventures "Chemical reactions?"

"Stop thinking about the lab for a minute," I say. "What's an *everyday* thing that you want to stay hot for a long time?"

Thoughtful silence for a second or two. Then, all at once, half the students in the room say "…Coffee!"

(Why yes, it is midterm season; how did you know?)

So this leads into a great discussion of the sorts of materials that are used for coffee containers and why they work well and others don't. Good times.

Even better: the heat transfer stuff lead to some examples with exponential decay, and investigation about why the energy vs time graph follows exponential patterns. After the workshop, two of the students asked for some clarification about exponential growth and decay--why does it do that? Why is the number "e" so important? It's not like the bacteria know about "e," do they? So I went into my usual explanation of what the derivative really means, how it relates to the basic prealgebra definition of slope, why it all works, how that applies to exponential functions, and why we use "e" as the base (short answer: it makes derivatives easier). The students just ate it up. One of them even showed up to my office hours later, asking if I could go over the meaning of a derivative again so she could think about it some more and make sure she's got it.

It took a while for that to really sink in: two students who have already been through calculus, and never need to take a math class again, voluntarily stuck around after an optional workshop because they wanted me to explain derivatives.

Sometimes I forget that my teaching skill really has improved quite a bit since I first started seven or eight years ago. It's nice to get a reminder of that every once in a while.
barnabas_truman: (math)
The whiteboard in my office is covered in stick figures named Alice and Bob who are riding fast trains and shooting lasers at clocks.

I like it when students come in for help with relativity!
barnabas_truman: (math)
The greatest progress is in the sciences that study the simplest systems. So take, say physics -- greatest progress there. But one of the reasons is that the physicists have an advantage that no other branch of sciences has. If something gets too complicated, they hand it to someone else. If a molecule is too big, you give it to the chemists. The chemists, for them, if the molecule is too big or the system gets too big, you give it to the biologists. And if it gets too big for them, they give it to the psychologists, and finally it ends up in the hands of the literary critic, and so on.

(from Noam Chomsky on Where Artificial Intelligence Went Wrong)
barnabas_truman: (army)
"So what is a free body diagram?"

"Okay, we're going to treat your cell phone here as if it were a single point."

"But then I cannot make calls on it!"

"Also it would then be inside its own Schwarzchild radius and thus collapse into a black hole! Aaaaagh!"


"Because it has nonzero mass but zero volume! Infinite density, u jelly? Yes u are jelly because you are crushed by tidal forces!"


"Except no wait you are not crushed by tidal forces because do you know what would happen to you if your cell phone collapsed into a black hole?"

"Nothing! Because its mass hasn't changed!"

"Yes! Hooray for physics!"
barnabas_truman: (army)
I pulled off a really awesome teaching moment in drop-in tutoring today. Towards the end of the time slot, there were only two students still there; one in Physics 7B (which is currently covering vectors, forces, and momentum) and one in Physics 7C (which is currently covering electrical forces).

I spent some time helping the 7B student practice drawing free body diagrams, in which an object is represented by a single point and all forces acting on the object are drawn as vectors emanating from that point. She seemed to be picking it up pretty well, so I left her with a few more practice problems and moved on to the 7C student.

The 7C student had been in drop-in tutoring before to get an explanation of the forces charged objects exert on each other. He was currently being puzzled by a problem about a balloon sticking to a wall due to an electrical charge, and having trouble understanding what force was holding it up. I suggested that he draw a free body diagram on the chalkboard, and right away he filled in the force of gravity pulling the balloon down and the electrical force pulling the balloon into the wall, but couldn't think of any other forces acting on it, meaning the balloon "should" move diagonally downward and into the wall.

"So is the balloon going to move through the wall?" I asked. No, of course not. "Then what force is keeping it from doing that?" He couldn't remember. "Do you remember doing free body diagrams in Physics 7B?" He smiled sheepishly and shook his head. At that point I realized that the only difference between this and a typical 7B problem was that one of the forces is electrical, and that was already on the diagram anyway.

Aha, I thought, I have another untapped teaching resource right here in this room!

"Hey, 7B student!" I said. "You're doing free body diagrams right now; what's keeping this balloon from pushing through the wall?"

"The normal force from the wall on the balloon!" she replied cheerfully.

"Exactly! And if there's a normal force mashing the balloon and the wall together, what other force is holding the balloon up?"

They chewed on that one for a while, and finally both got "Oh! Friction!" when I re-drew the diagram sideways (they're not accustomed to thinking of friction on a vertical surface). After that everything fell into place and the rest, as usual, was just algebra.

Thus having saved the day, I donned my hat and cloak and flew home.

Anyway I thought it was really neat that I was able to simultaneously bring together students from two different classes to solve one problem, give the 7C student a review of 7B material, give the 7B student a preview of 7C material, and let them both feel like they had accomplished something. I love my job.
barnabas_truman: (army)
A while ago I custom-ordered a bunch of Lego parts online. I had been looking for some sort of building toy so I could build frameworks to hold together the demonstration circuits I use in physics workshops, and the Technic pieces with holes for axles seemed like they'd be just the thing for keeping wires in place. Here's the result:

(The stack on the right contains a 9V battery in the upper compartment and a bank of capacitors in the lower compartment. The switch allows toggling between charging and discharging the capacitor bank through a buzzer, demonstrating exponential decay of current.)

On a whim, I decided to get some axles and gears as well. Between workshops and office hours, I occasionally spend some time in my office messing around with these delightful clockwork building blocks, and this is what I've managed to build:

The cream-colored gears have 20 teeth each and the black ones have 12, so each axle rotates at a speed 20/12 times that of the previous one. That means the final axle rotates at (20/12)^6 times the speed of the first (hey! more exponential growth!), or about 21 times as fast. I've ordered a few more gears and axles (I ran out) so I can fill up the rest of the block and get a 60x speed multiplier!

See it in action here:

barnabas_truman: (dwarf)
Just spent a decent chunk of office hours playing with Lego gears... and using them to explain important principles of mechanics to some physics students. I love my job.
barnabas_truman: (dwarf)
My Lego order came in!

But this time, instead of building the usual castles or spaceships or flying motorcycles or whatever, I put together a gear train that significantly steps up (or steps down) the applied rotational speed.

Then I took it apart and built a lost desert temple.


barnabas_truman: (Default)

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