## Wednesday, May 18, 2011

### This xkcd Comic Hit Home With Me: "Teaching Physics"

xkcd is a comic that tends to be a bit on the academic side but I think their warning disclaimer tells you better what this comic series about than I can:
"Warning: this comic occasionally contains strong language (which may be unsuitable for children), unusual humor (which may be unsuitable for adults), and advanced mathematics (which may be unsuitable for liberal-arts majors)."
Of course, this warning is tongue-in-cheek but it does give you a flavor of what the comic series contains.

My husband forwarded this comic from this a few days ago called "Teaching Physics" (click on it to see the full size image on xkcd.com):

Now, I have talked at length on this blog about doing education outreach at LIGO.  In that process, I interact with many students, teachers and people from the public and I use the 'rubber sheet' analogy often when describing that gravity it really an effect of the curvature of space-time.  However, this only works if one thinks about a real rubber sheet that they could interact with on Earth, i.e. there is still gravity around to pull masses down on the sheet.  Most people have no problem overlooking the fact that we are using gravity to describe the curvature of space-time but there are the few who bring up the paradox to me.

This is where I disagree with how the instructor in this comic handled the situation.  To me, the correct response is not to sigh and dismiss this useful (if imperfect) analogy.  Instead, I recognize that the observation is a valid one and compliment the person on being insightful (usually including that most people don't see the problem).  I then ask them to take the gravity around them for granted and just use the rubber sheet as a visualization tool.  After all, there are many analogies in physics but if you think about any of them for too long you start finding imperfections in them.  (Like using water waves to describe properties of light [electromagnetic] waves - a few problems with this include that water waves need a medium [water] to propagate and water waves are easily damped when light isn't.)

I'm not criticizing the author of this comic!  After all, I don't think this instructor is doing "outreach" as much as teaching in a formal education setting.  I've had a lot of experience there too and, depending on the student (like are they the kind that try to be difficult at every turn or are they truly being insightful), I very well may have had the same reaction.  And I just love that there is a comic out there that makes me jump up and say, "That's happened to me!"

1. It had never occurred to me to ask that question, though I understood that it was an imperfect analogy. I was always more preoccupied by how a 2 dimensional sheet is really a 3 dimensional "spacetime" ... thing.

I also love how the comic professor responds (though I certainly hope that nobody would do that in real life). I like the point that reality is whatever it is, and our equations are the best guess we have -- but even those are just "like" reality. They are our best guess, still subject to revision as observation dictates.

I also like the point that teaching is *hard*! It's all too easy to make it sound boring. Which is a shame, because it is so very cool and exciting! The best teachers capture that excitement, but it is hard.

2. I agree with you that teaching is hard! I have the utmost respect for teachers, especially those in primary and secondary education. They have to be on all day and be interesting to boot - oh, and be accountable for their students' learning outcomes. That is nothing to sneeze at!

I remember the first time I was given my own college class to teach. I picked conceptual physics (with very little math) since I found that the less math you can use, the harder it is to teach since you (the teacher) need to be able to communicate what the equations mean. For every 75 minute class I taught, I easily spent 3x as long preparing the lecture to be interesting and educational. It was a wonderful experience that I was lucky to have. That being said, teaching in college is *very* different than teaching primary and secondary students! If my students didn't come to class, that was their problem. If they didn't do their homework and performed poorly on exams, they got bad grades and that was the end of it.

3. I have experience with informal education, and your approach deeply resonates with me.

Shrugging off a student's analogy is counter-productive to fostering curiosity and learning. Analogies are how students learn new complex things, whether it's by using Mother Goose, sports, rubber sheets, or TV.

In contrast, as you wrote, you would have handled the situation well by complimenting the student on the analogy. An analogy, by definition, isn't the actual thing. Coming up with an analogy is a first step to figuring out the actual thing.

Great post.

4. Thank you! I am glad that you identified with my post! It feels good to get to communicate with others like me out there! (Hmm... Can I fit in any more exclamation points? Yes!)

5. I used to see this question a lot on Usenet. I used to tell people to imagine an object sliding frictionlessly along the sheet, not being pulled "down" by gravity, but being deflected by the curvature of the sheet itself.

The comic's alt text remarks, "Space-time is like some simple and familiar system which is both intuitively understandable and precisely analogous, and if I were Richard Feynman I'd be able to come up with it." But Feynman frequently objected to making analogies involving fundamental physics processes, since they were fundamental and couldn't be explained in terms of something simpler. See him wrestle with the question of how magnets work here.

6. Thanks for the new way to express the analogy!

And there are many out there who oppose the use of analogies and I agree with them (and Feynman) to a point. Any time I use an analogy, I make sure to point out that it is never perfect, usually giving an example of situations where the analogy fails. But I know from when I learned fundamental concepts the first time, the analogies helped bridge me into the deeper understanding. That being said, when I continued to rely of the analogy, I could become confused (like the plumbing analogy for electric circuits - I would sometimes let currents from different branches mix like a fluid could and it made it difficult to solve some of the complicated circuits with parallel branches). I am OK with the use of analogies only to introduce the concept and then stress that the analogy should be left behind at that point.

7. This blog post was restored after the Blogger outage between 12-13 May 2011. However, the comments for this post were not. I am manually restoring these comments from the notification emails I received when they were posted:

Charlie has left a new comment on your post "This xkcd Comic Hit Home With Me: "Teaching Physic...":

It had never occurred to me to ask that question, though I understood that it was an imperfect analogy. I was always more preoccupied by how a 2 dimensional sheet is really a 3 dimensional "spacetime" ... thing.

I also love how the comic professor responds (though I certainly hope that nobody would do that in real life). I like the point that reality is whatever it is, and our equations are the best guess we have -- but even those are just "like" reality. They are our best guess, still subject to revision as observation dictates.

I also like the point that teaching is *hard*! It's all too easy to make it sound boring. Which is a shame, because it is so very cool and exciting! The best teachers capture that excitement, but it is hard.

Posted by Charlie to Living LIGO at May 12, 2011 9:27 AM

8. stuver has left a new comment on your post "This xkcd Comic Hit Home With Me: "Teaching Physic...":

I agree with you that teaching is hard! I have the utmost respect for teachers, especially those in primary and secondary education. They have to be on all day and be interesting to boot - oh, and be accountable for their students' learning outcomes. That is nothing to sneeze at!

I remember the first time I was given my own college class to teach. I picked conceptual physics (with very little math) since I found that the less math you can use, the harder it is to teach since you (the teacher) need to be able to communicate what the equations mean. For every 75 minute class I taught, I easily spent 3x as long preparing the lecture to be interesting and educational. It was a wonderful experience that I was lucky to have. That being said, teaching in college is *very* different than teaching primary and secondary students! If my students didn't come to class, that was their problem. If they didn't do their homework and performed poorly on exams, they got bad grades and that was the end of it.

Posted by stuver to Living LIGO at May 12, 2011 9:41 AM

9. Jonathan has left a new comment on your post "This xkcd Comic Hit Home With Me: "Teaching Physic...":

I have experience with informal education, and your approach deeply resonates with me.

Shrugging off a student's analogy is counter-productive to fostering curiosity and learning. Analogies are how students learn new complex things, whether it's by using Mother Goose, sports, rubber sheets, or TV.

In contrast, as you wrote, you would have handled the situation well by complimenting the student on the analogy. An analogy, by definition, isn't the actual thing. Coming up with an analogy is a first step to figuring out the actual thing.

Great post.

Posted by Jonathan to Living LIGO at May 12, 2011 11:19 AM

10. stuver has left a new comment on your post "This xkcd Comic Hit Home With Me: "Teaching Physic...":

Thank you! I am glad that you identified with my post! It feels good to get to communicate with others like me out there! (Hmm... Can I fit in any more exclamation points? Yes!)

Posted by stuver to Living LIGO at May 12, 2011 11:39 AM

11. Thanks for restoring my comment!

12. No problem! I was disappointed that one of the few times I got a good conversation going was one of the few times that Blogger bugged out :(

Thanks for taking the time to share your thoughts!

13. the comic is very funny when you are just reading it but when you are the person that represent the teacher and your student act like that maybe you will kill your student. just joking. anyways i like the concept of your comic i have also triend to make some comics and posted at my friends blog --> http://paidcritique.blogspot.com/2011/09/how-to-make-runs-faster.html but its not funny. maybe my punch line is not good... :(

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