Archive for November, 2010

Physics Test

10 November 2010 at 3:42 pm
by Berck

Today was the day of my second physics test. I was rather apprehensive about the whole thing considering how I was crushed by the first test.

Things started to go wrong on Monday, when I accidentally dropped my backpack in such a way that it smashed the screen on my HP-48G. I didn’t love the HP-48G, but I liked it well enough. As a geek who went to high school in Texas, I learned to use an HP-32SII as part of the UIL Math/Science team, and suffered brain damage as a result. I can no longer use an algebraic (i.e., non-RPN calculator. Since I don’t know anyone who could let me borrow one, this meant I need to find a calculator, soon.

HP-32SII, despite being something like $30 new, are now going for nearly $200 on eBay for a nice. They were discontinued back in 2002. It might be the greatest calculator ever produced, but I had no way of knowing that at the time. I also didn’t know that when HP stopped producing it, they’d stop producing decent calculators in general. For years, there was nothing but the abomination that is the HP-33s available.

I never had my own 32SII, because I was always assigned one that belonged to whichever high school I was attending. In college, I borrowed one for physics exams, and never got around to getting my own. When I finally went to buy one, they were going for $100 on eBay. I should have bought one then. Instead, I opted for the 48G, which is basically the graphing version of the 32SII. This makes it way bigger than it needed to be, but it had the same basic keyboard feel and layout of the 32SII, so I was content. I never used the graphing functionality, as I don’t believe in graphing calculators, but I liked the big screen because it let you see several lines of the stack at once, which is probably the only thing I liked better about it than the 32SII. Unfortunately, the large screen also cracks pretty easily when it’s in a backpack that gets dropped.

I was going to replace it with another 48G from eBay, but even those seem to be going close to $100 for a nice one these days, and that wouldn’t get here in time for the exam.

But then I remembered someone mentioned that HP started producing what might be a decent RPN calculator a few years ago, the HP 35S. The Amazon reviews included a lot of former 32SII users forced to “upgrade”, and were generally favorable. Furthermore, with Amazon Prime, I could have it shipped next-day for only $3.99, and it would get here in time for the exam.

It did, and it’s an okay calculator. It has a seriously annoying display bug wherein it will display something like 1.60245856345×10-19 as “1.60245856345E-” and then you have to hit the right arrow key to see the rest of it. Which is phenomenally dumb because no one’s going to care about the last few significant digits, but everyone’s going to care about the magnitude! It would have been trivial to make it so that the “E-19” is always displayed, and you could scroll to the right for more digits. Things like that make me think HP may never make another good calculator.

The physics test was relatively easy this time around, except for one problem. I’ve reproduced it here. (Note my mad circuit drawing skills, which I needlessly acquired just for this post.) The only text with the problem was the following:

Find the current through R2.

No problem. I couldn’t believe the luck that this was one of the two big-points problems. I just needed to find the equivalent resistance between R2 and the and the 20Ω resistor in parallel with it. Then find the current through the remaining 3 resistors in series, which would give me the voltage at either side of the parallel resistors, and then the current through R2. That’s when I realized he didn’t tell us what the value of R2 was!

I stared at it. No wonder it seemed too easy. But how to solve? Maybe he didn’t want a number, but rather an expression for the resistance? It’d be an ugly expression, but I set about writing it. Then I thought maybe there was something fancy I could do with Kirchoff’s Laws, but what? I started writing down loop and junction equations to see if there were was some way to figure it out. It became obvious that was just going to make the problem worse, not better. Why couldn’t I do this? What trick, equation or law was I forgetting that would let me figure this out for an unknown resistor? I did every other problem on the test, then came back to it, and was still stumped.

There were about 15 minutes left on the test, and only a couple people had turned in their tests. I’m pretty slow and methodical, so I was surprised almost the entire class was still in the room. I figured they were probably all struggling with the same problem, so I didn’t feel too bad about it, and settled on writing down everything about the circuit that might be useful in hopes of getting some partial credit. With about 15 minutes remaining, someone went up and asked the professor something.

He walked to the white board and said, “Uhm. Sorry. Sorry. On Problem 1, R2 is equal to… err. What number would you like? How about 10 ohms? I’m really sorry about that.” There was an immediate groan, and a lot of laughter as we looked around the room at each other, realizing that we were all in the depths of the same completely pointless hell. If only any of us had asked earlier! There was amazingly furious erasing for the next 30 seconds, as I suspect all of us had covered the entire page in nonsense hoping to crack something. Of course, with the missing resistance provided, the problem became nearly trivial. Definitely one of the most amusing test-taking moments I can remember.

There was a fun problem I hope I got right that went something like this: “The winch on my jeep draws 50 amps from a 12V battery. How much power does it draw? If it weighs 2000kg, how long would it take the winch to winch the jeep up to the top of the library tower (30m)?” Cute. The first part is easy. The second part involved dredging up things from Physics-I I’d forgotten a decade ago. I managed to come up with U=mgh, so I knew how much energy (Joules) would need to be expended by the winch, but how long would it take? Where was time in this problem? Then I remembered: current is dq/dt, with units of Coulombs/second and it all fell together. Not a difficult problem, but cute. There might have been a more elegant way to solve it, but I’m pretty sure I got it right.

Virginia is for Lovers (again)

8 November 2010 at 8:36 pm
by Berck

This time, Noell got married.

There aren’t many people for whom I’d hop an airplane and fly cross-country just because they sent me a wedding invitation, but Noell is one of them. Sydney feels similarly, so Sydney, Jonah and I split a hotel room and rental car.

Sydney got in a little late, and Jonah and I got in a little early, which means we got there at about the same time. Sydney met us at the rental car counter, where she realized that she’d declined insurance and listed herself as the only driver of the car. She doesn’t have auto insurance, because she doesn’t own a car, so we decided this wasn’t brilliant and waited for her to change it. The quickest solution was for her to buy the insurance and keep the car in her name. This was fine with Jonah and me, because this meant Sydney was the designated driver for the weekend. She didn’t realize this until later.

Sydney also managed to leave her contact solution at home, so I found a 24-hour Walgreen’s on the Droid. We walked into the store at about quarter to midnight, and Jonah and I picked up a box of cold Yuengling while Sydney examined the contact solution options. We brought the beer to the front of the store, and the guy at the register said, “It’s almost midnight.” “So?” He just stared at me. “Is there a problem?” I asked. “You can’t buy beer after midnight.” “Well, it’s not midnight!” He scanned the beer and showed me the register screen which said something to the effect of “TIME RESTRICTION”. I showed him my droid, which demonstrated that it was still 11:57. He wouldn’t even get a manager. I really hate Virginia.

We slept until lunch time, then got lunch with Jonah’s Uncle at The Black Sheep. It’s rather popular and small, so we had to wait for over an hour for a table. Fortunately, they let us wait on their patio with drinks. The food was good, and the menu rather eclectic. For instance, Jonah got the “Roast Duck Hash,” which was pretty good. I simply got some biscuits and gravy, but they were excellent.

After a very long lunch, we got back to the hotel with just 15 minutes to get ready for the wedding. We managed, and got to the church with a few minutes to spare. It turns out that girls can’t actually marry each other in a Presbyterian church, so it wasn’t really a wedding. But some officials in DC were nice enough to marry them a couple of weeks ago, and since Noell’s a Presbyterian minister (working at a Baptist Church?), she wanted to get “married” in her church.

The reception was at an art gallery, and there was an ample supply of Abita. I made a valiant effort to deplete it, but to no avail. I got to see Noell’s parents, which was fun, but didn’t know anyone else there. Jonah made me dance, and some girls who were seriously impressed with my beard were strangely impressed with our dancing. I can’t dance.

After we got back to the hotel, I asked Jonah when our flight left. “12:35,” she announced. “What? Surely not that early.” “No, that’s what it says,” Jonah announced reading from her computer. Sydney said, “I’m leaving at 2:50, and I really thought our flights were at the same time.” I said that I thought so too, but Jonah assured us we were wrong. We decided to leave the hotel at 11am, so Jonah set her alarm or 10:00am. It didn’t go off, but Jonah woke us up by opening the blinds when the clock said 10:00am anyway. After awhile, she finally realized that it was actually 9am, so we could sleep another hour. By then, though, I was too awake to go back to sleep, so I gave up and showered. I logged on to the delta website to check us in for our flight. Which was scheduled to leave at 2:50pm.

Jonah apparently decided our flight number was our departure time. You’d think I’d stop believing Jonah when it comes to transportation schedules, but I keep falling for it. Luckily, all that happened is that we missed out on brunch with Noell, and woke up too early.

Our flights back were plenty miserable, but fortunately nearly on time, as compared with the 5 hour delays on the same flight the week before.

Sometimes I Win.

3 November 2010 at 8:23 pm
by Berck

It doesn’t seem like often, especially lately.

I have 4.5 hours between classes every day. Initially, I thought this was going to be a terrible schedule. In actuality, things have conspired to make it an excellent schedule. Because I ride Yoshiko (the little Honda) to school everyday, I’m somewhat disinclined to ride home between classes. Each ride involves a fairly lengthy procedure of getting geared up then getting undressed at the other end. It just seemed safer, and cheaper, and more green, and mostly just easier to stay at school between classes. So I spend the entire time in the library doing school work.

This has transformed me from a truly awful student to a pretty good one. I still don’t really take notes, and don’t really know how to study for a test, but I do okay. I’ve got a solid A in 3 classes, and a B+ in the other one, which isn’t bad, all things considered. It varies from week to week, but most of my time is either taken up with Physics or Calculus. I’m doing astonishingly well grade-wise in Calculus, but the grades feel inflated. On the other hand, half the class has dropped, and I’m not sure how many of the others are actually passing.

I spent nearly all of my 4 hours on Monday working on Physics homework that’s due today. I had a bit more trouble than usual since I was in Highlands during the lecture Monday and Wednesday where I should have learned about RC Circuits. I spent most of my 4 hours on Tuesday finishing the physics homework. On Tuesday, I talked with a couple of my classmates about one of the more annoying problems. They agreed it was difficult. I eventually got to a solution on the worst of them, but it required a linear system of 6 equations with 6 unknowns. Which I could probably solve by hand, but which would take hours. So I let Wolfram Alpha do it for me. I got the correct answer, but there’s surely a simpler solution.

Before class this morning, one of my classmates asked if I’d figured it out. I told him about my cop-out, and he said he had a much simpler solution. I reached into my backpack to pull out my homework and discovered that I’d left it sitting on my desk at home. Which really sucks. Hours spent doing homework that now I couldn’t turn in. Not wasted hours, since I needed the practice with the problems, but still seriously annoying that I wouldn’t get credit for it.

I thought it was a bit strange that my physics professor didn’t wander outside for his pre-class pipe smoke. I often sit outside until he’s done smoking his pipe, since obviously class isn’t going to start before then, and sitting outside is generally much more pleasant than sitting in a hot, stuffy, and ugly lecture hall. When he walked into class, he didn’t have his physics book. He said, “Sorry guys, I feel like crap. You can just turn your homework in Friday.” And then he walked out.

So, the day I don’t have my physics homework is the day that class is canceled and homework is due the next day! One of my classmates asked, “Did you poison the professor?”

The even better part is that I needed the time. Since Jonah and I went to Highlands, NC last week, I had all kinds of things to catch up with. Worse, Noell is getting married this weekend, so I don’t have the weekend to do anything. I have a physics test the Monday morning I get back, and Calculus due Friday. With my extra time today I was able to not only finish the Calculus homework, but also finish the programming assignment due on Monday. Which means I’ve got plenty of time to study for Physics tomorrow. If only I knew how to study.

On the one hand, it’s been fun learning things. On the other hand, I’m a pilot, aren’t I? It’s been almost a year since I’ve flown an airliner, and a six months since I’ve been in an airplane. And I’ve got do this for another couple of years before I can graduate. Is it worth it? Can I afford it? I really don’t know. The deferment on my student loans from a decade ago finally went through. Getting a degree pretty much ensures that I’m going to be paying back student loans until I die.

I’m not at all sure this is a good decision. But I’m not sure what else to do.

It’s been a rough week, and I’m seriously looking forward to first Thanksgiving, and then the end of the semester. So I can do it all over again?