Monday, May 9, 2011

Addressing Misconceptions II

In a previous post, I brought up a question from @thinkthankthunk about a common student misconception about gravity:

"How to address this student misconception? Atmosphere is necessary to create gravity"

My gut-response tweeting at the time was this:
"Engage with it: Ask them to elaborate on their idea... ask them draw pictures, to help explain how it works..."

followed by, "There is a meaningful correlation: b/c gravity is pulling, there is a lot more air near the earth. [It's] just not causal."


"Oh, and air collectively pushes UP, because it provides a buoyant force. So maybe helping student to see that?"
Now I've had time to digest it a bit more

First, it has been and continues to be a struggle for scientists to understand phenomena that seem to involve actions occurring over a distance. While Newton's framework for gravity proposed a universal law of gravitation that acted instantaneously over a distance, physicists have worked hard not to do so. Physicists invented the concepts of electric and magnetic fields, partially because they function as intermediary objects that span distances. In the field view, the field at a point responds to neighboring points in such a way that disturbances propagate at the speed of light. In a somewhat alternative attempt, physicists invented intermediary particles like photons to function as energy and momentum carriers over those distances. With gravity, general relativity proposes that space itself is a intermediary that changes in response to mass, and those changes, too, propagate at the speed of light. In contemporary quantum physics, physicists and philosophers still don't fully grasp the causal implications of quantum entanglement, because they seem to imply "spooky" actions at a distance.

Second, it seems relevant to think of air molecules as carriers of momentum and energy, and thus could be considered force carriers. For example, air is the medium responsible for drag and buoyant forces. The interesting thing about the student idea that air causes gravity is that, in their idea, somehow the air causes a downward force. Perhaps they are focusing on how air pressure pushes down? Well it does push down, it just happens to also push up, and to the side, and every which way. In our mind, objects experience an upward buoyant force due to air as a result of all that pushing. What do students think? We can only know if we ask and engage.

This is a bit of why I tweeted, "Engage with it". If I don't know why my students think atmosphere is necessary for gravity, I don't know enough about their idea to know what to do next. If my students don't know why they think atmosphere is necessary, than it's probably worth while asking them to elaborate and make drawings. They have to come to know their mind.

In my mind, given that (1) gravity seems to exist where there is atmosphere, and (2) gravity seems to have no visible causal mechanism, it seems perfectly natural for a person to infer that air plays a causal role in the effect of gravity. In students doing so, it's possible we are just seeing their commitments to empirical regularity and to causal mechanism, both very important pieces of doing science. If students are struggling to see spooky action at a distance, then perhaps they are being equally as skeptical as scientists have been for hundreds of years. Certainly we may think that students are crazy for thinking atmosphere creates gravity, but isn't it weirder to propose massless particle called "gravitons" or curved spacetime

In fact, it was without the weird notions of fields, gravitons, or curving space-time, that Newton had little choice but to give in to empirical and mathematical coherence of the universal law of gravitation. His law fit the data. But, keep in mind, that Newton could only do so when more empirically precise data of moving planets was made available by better optical instruments and calculus was available to understand better how that data could be made sense of in terms of the rate of rates of change. While causal mechanism was abandoned at the time, it was reintroduced later when new concepts and mathematics allowed for it.

What's the point?

It's tempting to think that students' wrong ideas can be simply described as misconceptions concerning an isolated topic X. I am always skeptical of that position.

In this case of atmosphere causing gravity, students' ideas are entangled in a large web, including the notions of action at a distance, causal mechanism, empirical precision, astronomy, rates of change, buoyancy, air pressure, spacetime, particles as force carriers, etc. In that web, they are entangled with the historical and contemporary puzzles in physics that have not fully been resolved. Certainly they are just beginning to make contact with those puzzles, but I believe it is our job to help students make meaningful contact with puzzles that arise in the web. It is our job to help them become better navigators of that web.

All and all, I think I would be tempted in a class to pursue these ideas (which seem to be about gravity) through buoyancy. Overtime, by helping students come to see air as providing an upward force, student have a genuine puzzle to resolve on their own terms: if air pushes up, what's pulling down? If not that route, I would simply "engage with it", by saying, "That's a good idea. How would that work, air causing gravity?"

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