The power of extra credit

I've been wrestling recently with how to keep better attention when I'm trying to show my kids something cool. For my most recent talk, I suggested to Mr. Lancaster that I be allowed to offer extra credit problems to the students, based on what I was talking about, in order to nurture those fledgling attention spans. We settled on three extra credit questions, interspersed throughout the talk, each worth the same as a homework assignment.

I am both impressed with how well it worked, and distressed by how challenging some of the problems were to these students. Since many of the kids in the class are new from last semester, I gave an updated version of my "Who I am" presentation, talking in general terms about my research, about rockets and space propulsion, plasmas, satellites, vacuum chambers, and moon rovers.

I like to try to get students involved when I give a talk, and since my talk was going to be about plasma rockets (Hall thrusters, for the advanced reader), we began with talking about what a plasma was. This worked pretty well, because almost everyone has heard of a plasma TV, and at least one student knew that stars were plasma too. (I thought that was pretty impressive!) So I told them about a bunch of different things that use plasma, like neon signs, plasma TVs, CFL bulbs and welder's arcs, and also about some in nature, like lightning, the sun or the aurora. This led to our first extra credit question just a few minutes later -- to recall four of the seven or eight plasmas we had discussed. I was pretty pleased with this as an easy introduction to the format for the questions, plus I was sure someone could get it right, and referring back to information like that helps reinforce it in students' minds. In both algebra classes, someone got it right.

I moved on to talking about rockets, and about how the space shuttle uses 6 gigawatts of power when it lifts off. This was a pretty good opportunity to explain about words like giga, mega, kilo, and also milli, micro and nano. I tried to get the class to think of words that use these prefixes, and they didn't do too bad. With the prompt of computers, 2nd hour came up with giga, mega and kilobytes, and of course the iPod nano got a mention. But for our second extra credit problem, asking how many 60W light bulbs would be equal to the space shuttle's 6 GW, there was a bit more of a struggle. Both classes eventually got it (mainly by guessing, I'm afraid... the answer is 100 million), but I think I could have done a better job talking about the different scales. Those numbers are awfully big to think about without a really firm grasp of the way you jump by a thousand between each scale, and I don't think I laid that foundation well enough to make them comfortable with all the zeroes in 100,000,000.

What I like best about presenting is that, if I can get the students' interest, some will ask questions that let me branch out and address their interest individually. For example, when I asked everyone to tell me what they thought of space, they came up with a lot of great descriptions (black, cold, way up there, empty), but one person also said, "no gravity." I let that slide for a minute, but later when a person asked how fast rockets went to get into space, I elaborated about escape velocities, and explained how something going fast enough would fall at the same rate as the curve of the earth fell away, so it never hits the ground. So, being in orbit is like being in free fall, hence the apparent lack of gravity. It's a good sign that the kids felt comfortable asking questions, and when I can answer one it helps cement their attention.

In fact, Mr. Lancaster and the student teacher Mr. T both commented on how today, after I gave my talk, was the best behaved 2nd hour has been all semester. So, I either bored them to sleep, or else I gave them something to think about that made class seem shorter and more relevant. Let's hope for option (b).

I also told the students about my lab, to get them interested in the field trip there at the end of the semester, and I explained how the lunar rover was tested in our vacuum chamber back in the '60s. For the last extra credit question, I looked up how far the rover had travelled on Apollo 17, and asked the students to figure out its average speed when it went 22 miles in 4 hours. 2nd hour got this one right away, but 4th hour never did get it at all, even after (literally) about 20 guesses. It's 5 and a half, and it's a little distressing that 22/4 was that difficult for them.

Of course, they didn't have their calculators.... but that's for another post.

I thought this went pretty well, using a combination of extra credit problems and frequent opportunities for involvement ("What do you think of when you think of a rocket", "Can anyone think of a word with giga or mega or kilo in it", "Tell me what you know about space", etc.). I was also able to make a pretty good connection with the current class material, which has been heavy on word problems and distance = rate * time type stuff lately. All in all, one of my more successful attempts.