Images, Resonances, Echoes, take 3

Some reverberations, some new ripples

Images- of multi-step arguments, unpacked, a graphical language, meta-physics

Many driving factors encourage pushing ever onward(I've experienced nerves, classroom management strategies, statement packed specifications). Yet, in encouraging a critical response to knowledge, you'll need to make rather a lot explicit and so open to comment and inspection. Otherwise , there is little to get a grip on. But continually shifting perspective to point out the structure of the argument can get wearing, particularly if talk has to carry all of the burden (the channel gets congested: bandwidth overload). Here is a moderate suggestion for using diagrams to represent the structure of the argument. There is a hope that used often enough it'll available as a resource to support discussion without having to be explicitly injected into the word-stream.

Start with distinguishing between the physical and the conceptual, choosing a defensible boundary: I'd suggest that every useful step of an argument can be put in one of these two buckets.

Physical (green): tangible, identifiably and uncontroversially a part of the lived-in world, with only a little structuring.

Conceptual(blue): a part of the imagined world of physics – precise created entities interact in defined ways.

Physical and conceptual steps

Next consider the kinds of transitions from step to step. You might get away with as few as four. SupportingPhysicsTeaching showed that this can be done with: intervene, evolve, redescribe, step.

Four kinds of transitions between steps

A moderate number is better(to support familiarity and therefore easy recognition), but this schema may be too parsimonious for you.

An intervene transition emphasises some intervention by an experimenter, so the panes either side are likely to represent the change between the "before" and the "after".

An evolve transition suggests that the process goes along by itself, without such outside interference, that we're watching the process evolve, so the panes either side might represent snapshots in that process.

The redescribe transition moves from one kind of description to another, for example from using forces to using energy, or from a physical to a conceptual description. Perhaps "now see it like this".

The step transition is a kind of catch-all, for when complexity or internal logic suggest inserting a break in the flow, but without any particular conditions being satisfied. You could think of it as a graphical paragraph marker.

And embedded in the distinctions is a view of what doing physics is: that too needs to be defensible, but as philosophies of physics differ don't expect a unique set to be self-evident. Maybe, for our purposes, the most important criterion is whether your particular schema is heuristically useful, or not.

It may be that an underlay showing just the structure makes more plain the forest-scale landscape of what thinking in physics is all about, blurring the trees.

Showing just the structure

Such diagrams can be hand drawn, but you might be better of having to hand a library of representations: here is one such, to get the ball rolling.

PDF representations

Of course you might prefer the flexibility of code (also enabling interactive diagrams, in which case a set of primitives like such as:


might form better building blocks with different granularities. But maybe that's a story for another time.

More reading

Multimodal communication

Ogborn 1996 Explaining Science In The Classroom Paperback Open University Press

Resonances- an account of why things float or sink

This is a classic multi-step argument, so long as you avoid the dead end of the traditional formulation of "the upthrust is equal to the weight of fluid displaced". The quantity and quality of physical insights in this sequence is itself a good reason to avoid that formulation.

You might start with a very physical experience of making a hole in water by pushing a ballon into a pail of water, and experiencing upthrust.

Then maybe supplement this with doctored bottles, some with holes in the side so that the bottles don't make holes in the water, others without such holes so that they do makes holes in water.

Then develop a line of argument somewhat like this:

You're going to think about making holes in water, using boats. Making these holes results in a buoyancy force on the boat, which supports the boat and its cargo. Buoyancy forces only occur in fluids, so you'll be thinking about pressure and the particles of the fluid bombarding the surfaces of the boat. To think about bombardment on surfaces, we'll choose to make a simple boat. You'll be concentrating on the surfaces at the sides and the bottom.

Making holes

Let's make a really simple boat, to reason with.

A simple boat

In a fluid, pressure increases with depth. So the sides of the boat will be at the same pressure, but the top and bottom will be a different pressures.

Pressure and depth

As the pressure increases with depth, so the bombardment gets more intense. Therefore you might expect different surfaces of the boat, at different depths, to experience different bombardments on each piece of exposed area.

Collisions and depth

Focus on a surface, and vary the pressure on either side. Increasing the pressure increases the bombardment. A difference in bombardment results in a force.

Differential bombardment

Note that there are both the bottom surface and the two surfaces that make up the sides of the boat to think about.

Forces combined

You could wrap all of these together, as a sequence of panes, with guides to link panes. Not to replace teaching, but maybe a resource for a flipped classroom?

A buoyancy sequence, with guide

A sequence, without guide

More reading

Scott McCloud’s infinite canvas

Echoes - an experiment and things past

A sideways thought, putting that well known supply of absorbers, textbooks, to use. Show fractional decay with a microwave source and detector by placing increasing numbers of textbooks between source and detector.

I liked this for a fractional decay show and tell, to accompany the books:

Adding books

As final reverberation for waves, combine the ideas of multiple step arguments, of story spaces to support flipped classrooms, to get:

The component ideas of a wave

Different wave patterns

Pulses and waves

That leaves the steps and superposition branch rather less developed. But IRE01 provided a sound basis for developing that line of thinking.