Thursday, March 13, 2008

Revamping Intro Physics Laboratory - Part 3 (Follow-Up)

OK, I got some very interesting responses to my suggestion of an experiment that can be done for an intro physics lab. I think I didn't explain myself too clearly on the premise and how I'm going to present it on here, so I should do that now.

While I tried to be explicit in describing the experiment and what would be a good way to do it, I don't actually want to reveal the whole hand. That's why I went along with the idea that there could be a dependence of the period with varying weights, because that is a very likely path that the students might attempt. If someone is thinking of actually trying to introduce this experiment in an intro lab, I don't want the possibility that some student might google it and find my blog where the whole thing has been revealed. :) That would defeat the purpose of them doing this without any kind of "previous knowledge".

So while I'm trying to be as clear and complete as possible in the experimental description, and the "philosophy" behind it, I don't really want to reveal everything either. In fact, I'm hoping that there WILL be students who decided to figure out if they can do it by changing just the weights. I consider discovering something that cannot work to be very educational. In fact, in science, knowing what doesn't work can be quite important (re: Michaelson-Morley experiment). They at least now know that changing the weights would not work. If they are curious enough, they'll try to find out WHY it doesn't work, and this is where the physics can be introduced.

Note that the experiment that I had suggested does NOT require that they have learned anything in intro physics. It is quite independent of the lesson they might have received in class. So in principle, this experiment could be done even during the first week of class. It doesn't require that they had learned about simple pendulum.



Anonymous said...

Two comments,

1) at UT Austin, they have one lab called discovery lab. The students have a lab manual with some theory on the quantity or effect they will measure, but no info on the experimental setup. The students then go, and try to get results. While this is a theoretically nice approach, I thought labs were there to reinforce the theory learned in the lecture and not to discover anything new (some people might learn something new, but only because they are not that good in the lecture). Discovery labs might increase interest in physics, but not necessarily teach more or better, specially when they have no theory behind it.

2) This is related to the last sentence of comment 1. Without any theory or mathematics, it is impossible to realize what to plot. For example, you mentioned in your previous post that they would figure out they needed to plot T vs. L, and then extrapolate to find the best result. This wouldn't work, and unless their mathematics background is extremely good (which is usually not the case) they won't realize that it is a square root. Maybe if they're told that T^2 grows linealy with L they have better chances of getting the right answer, but this means that in a way you are telling them T doesn't depend on M.

Interesting approach, not sure it can work though.

ZapperZ said...

If you examine our everyday lives carefully, you'll notice that there are many things that we have to decide and figure out. Often, these can be done in a systematic manner in physics, but when we are doing it either at work or at home, we tend to try to figure things out quickly without realizing that this CAN be a physics problem.

I'm trying to get across the message to the students that physics isn't simply confined to some sophisticated, esoteric experiments that have no connection whatsoever with the decisions they make in real life. In fact, they have have employed physics in doing certain things in a certain way already without realizing it. That's why I give them what appears to be a trivial exercise which can be solved without knowing any theoretical background on the physics of simple pendulums. That is the whole point of this exercise.

It is OK if they don't have a straight line curve to look at. All I care about is that they see a trend, or a relationship, between the two variables. In many experiments, knowing how something is related to something else is of utmost importance. The students can easily sketch freehand to extrapolate in between the points.

Again, while we tell them that they have to do this as accurately as possible, what we as instructors should emphasize on is not the accuracy of the results, but HOW the results were obtained. I am more interested in finding out what they did, and WHY they did it that way. What exactly were they thinking that made them chose certain decisions in trying to accomplish this task. When we have succeeded in making them think of the various step they take, we have accomplished the major portion of our task to make them think systematically and "scientifically".

To me, that is the most important accomplishment we can get out of these intro physics labs.


Anonymous said...

Anonymous #1 again. I agree that stimulating the brain by making them think is a good a idea. I am just not so sure of how much liberty you can allow in science, particularly in physics. If the students are not science majors then it's ok. They will probably learn more by doing discovery labs. On the other hand, if the students are science majors, specially physics majors, I think intro physics should give them a solid background. Some might argue the lectures are for that, and for the most part yes, but I think a lab that reinforces the topics learned in the classroom serves more to a physics student than promoting their interest for science (which presumably is already there given they chose physics as their major).

ZapperZ said...

If a typical intro physics lab only has physics majors, then I might tend to agree. But the majority of students in an intro physics class are not. In fact, in smaller schools, there are only one intro physics class that everyone that needs physics are required to take. So the labs are targeted to them.

Still, I also believe that physics majors can gain a lot out of something like that. As an experimentalist, I'm trying to convey to them that many problems in physics are that open-ended. Not only do you not have a "right answer", you also need to figure out how to do it.

Furthermore, I don't quite see how doing an experiment on a physics principle reinforces what they learned in class, even though that is the intent. I know that when I was doing such a lab, I never gained any better understanding of what I was learning in class simply because I was seeing it being illustrated in the lab. And from what I've seen while I was a lab TA, most students (if not all) didn't get that either. All they wanted to do was complete the lab as fast as possible and get out of there.

Note that the lab CAN, in fact, have the option to introduce the physics principles at the end, or as a part of a discussion. If the students tend to measure the pendulum's period by swinging it over a large angle, depending on how accurate it was measure, he/she will see that the period would not keep time as well as when it is swung over a smaller angle. The instructor can then introduce the simple pendulum physics and the small-angle approximation that gives us a simple relationship between the period and the length, which isn't valid when it is oscillating over a large angle.

So yes, one can still include relevant physics in here. It is just isn't my main aim in the exercise of revamping the physics labs.