Monday, December 22, 2008
Using Science Labs to Teach Science
If you walk into a typical physics or physical science classroom that's about to have students do a simple pendulum experiment, you're likely to see the formula for the period of a pendulum on the board. What you're unlikely to see is any discussion of experimental error or of how to make scientific observations.
Because it's so crucial to learning science, I'm going to discuss how to teach science using science labs. I'll use the example of a simple pendulum experiment because it's well understood. (By the way, those science teachers who make the extra effort to do experiments correctly deserve our praise and support.)
In a typical class, after explaining exactly what a simple pendulum is, teachers will show the formula for the period of a pendulum. They may have to explain about period and frequency. They will then point out the the formula for the period of a pendulum does not include the mass of the pendulum bob and that the period increases as the square root of the length. The effect of amplitude may not even be mentioned.
The experiment directions have been carefully written so that students make no mistakes. They start the pendulum moving with small swings and time ten swings. The length, mass, and period are recorded in the student notebooks. They then take measurements using other lengths and masses.
For many students, this experience is quite unsatisfactory. They've been asked to obtain a specific result. If they do not obtain the desired result, their grades suffer. Of course, many students appreciate the opportunity to get out of lecture and do something with their hands. Some even enjoy the detailed task of counting and recording. Neither of these rationales has anything to do with learning science. An excellent opportunity to learn science has been wasted.
Now, imagine another scenario that does play out in some of our science classes but in too few. The teacher begins by explaining some vocabulary such as period and frequency and eliciting some answers from the students. Next comes a discussion of what a pendulum is and some history about Galileo watching a chandelier. The teacher guides the discussion into how Galileo timed the period of the swinging chandelier. They didn't have clocks then so he must have used his pulse. What was his precision?
None of this discussion reveals the dependence of the period on pendulum length or mass or even on swing amplitude. Next, the teacher presents the class with the experiments they will do. What are the independent variables? Of course, there's the parameters of length and mass. What about amplitude? The dependent variable will be the period.
How will students measure pendulum length? What is the position at the top from which they will measure? What is the bottom position? Why choose these positions? Student ideas should be heard on all of the significant experimental details.
How will students measure the dependent variable? For the simplest case, students will time a number of swings. The class can discuss how many swings. What are the pros and cons of more or fewer swings? Should you use the lowest point or highest as the trigger? Different students may choose different strategies and discuss the outcome after the lab is over.
For students who also have the Smart Science® Pendulum Investigation lab unit, they can analyze data collected at intervals of 0.10 seconds. With many more points, they'll have greater precision. To get that precision, they must find a way to extract the period from the pendulum bob positions. That could be quite a challenge if they wish to use all of the points to maximize precision.
An advantage of the virtual lab will be in seeing the shape of the curve produced when position is plotted against time. As students take each data point, the graph develops and students see a sine wave appear. Notice that the sine wave comes from the data rather than vice versa as in simulations. Simulations are backwards and should not ever be the object of student scientific investigations.
Teachers can lead discussions about the implications of this wave shape for when the pendulum is moving fastest and when its moving slowest. The relationship with kinetic energy can readily follow. For more advanced classes, the nature of acceleration during the swings can be discussed and can lead to analysis of the changes in force because force is directly related to acceleration.
Students collect their data as they have planned, carefully entering the numbers into their laboratory notebooks for later analysis.
Once the students have their data and have analyzed it to come to specific conclusions, it's time for the class to compare and discuss the results. The teacher acts as moderator while calling on different students to present their data and conclusions. Teachers should guide students carefully to accepted conclusions while emphasizing the nature of scientific investigations. Empirical work is subject to errors and ambiguity. What possible variables were not controlled or measured? How might they have influenced the conclusions?
At the end, the students will remember the subject matter much better for having discovered it this way instead of simply being told the "facts." However, much more importantly, they will gain a better understanding of the nature of science, of how science works, and of what scientists actually do. As a result, we can hope that more of them will choose science or some related area as a career. We can hope that as future citizens, they'll better be able to make the decisions that we expect our informed citizenry to make.
We're facing an uncertain future. We cannot know what tomorrow will bring. We do know that having a good understanding of science will add another tool to everyone's mental tool kit to help them when the unexpected does happen. In the meantime, having Carl Sagan's "baloney detection kit" will help them every day to live better and happier lives.
© 2008 by Paracomp, Inc., U.S.A. www.smartscience.net
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