Notes Toward an Imaginary Class on Cartoon Physics
Using bad physics to introduce actual physics.
Over on Twitter, Nathan Pyle of Strange Planet fame did a post asking about “cartoon physics,” which I was initially inclined to be slightly snarky about, but then I changed my mind:
(This is a thing that I do— I randomly latch onto some passing idea and consider it as a pop-science/ non-majors course hook. Because apparently I don’t have enough actual work?)
I don’t really have the time to do this in detail, but I thought I’d throw up a couple of sketches of what I mean, just for fun. This is just a thinking-out-loud sort of post, because I can do that here if I want to. So, here are a few examples of how cartoon physics might work for introducing real physics ideas:
The Equivalence Principle:
Starting with Pyle’s original example, there are a bunch of ways you could go with this, but the deepest of them is the idea of the Equivalence Principle. Formally, this is the idea that the inertial mass (the “m” in Newton’s second law of motion) and the gravitational mass (the “m” in Newton’s law of gravitation) are the same. More practically, this is the principle that tells us that all objects fall at the same rate— as you make an object heavier, it gets harder to accelerate but the force of gravity on it increases at exactly the same rate, so the net effect is no change in the acceleration.
This was an empirical fact in Newton’s day, but didn’t necessarily have any justification, and there were a number of efforts to test it, most notably some really impressive experiments by Baron Loránd Eötvös testing different combinations of materials to see if there was any difference in the gravitational attraction between them. This was elevated to the status of a fundamental principle when Einstein was working on extending relativity to accelerating motion— he later called this the “happiest thought of my life” (in German, though)— and was the inspiration for connecting acceleration to gravity in the theory of General Relativity.
So, the fact that real accessories don’t do fall at different rates than their cartoon counterparts is an illustration of one of the most profound and influential theories we have.
Inertia:
The other way to approach the “delayed falling of accessories” is through the idea of inertia more generally, but I think that’s maybe better done through another classic trope: characters getting literally knocked out of their shoes. This is maybe the closest any of these come to real physics— it’s Newton’s first law of motion, that an object at rest tends to remain at rest unless it’s put into motion by an external force.
That’s the germ of a real idea hiding behind the shoes joke, and also things like the classic slinky drop, which you can find in numerous forms on the Internet, but here’s a still from a version with my kids when they were much smaller than they are now:
I would also recommend this high-quality version from Derek Muller of Veritasium, which includes a horizontal version that’s more analogous to the knocked-out-of-shoes thing.
Perspective:
The other one that jumped out at me in the context of thinking about this as an imaginary class is the classic painted tunnel. There’s probably some opportunity with this to bring in a bunch of optics stuff, about how and why trompe l’oeil paintings work, even if you can’t actually run through them. That could be of interest to students who aren’t science majors in a way that the equivalence principle maybe isn’t.
I’d need to do a bunch of background reading and stuff before I could really talk sensibly about this kind of thing, though. Which is why it’s likely to remain only an imaginary class topic…
That’s three examples, which is the canonical number of Things that make a list, so I’ll stop. It’s entirely possible that I’ll end up turning one or more of these into an actual blog post (probably for Forbes), but that would depend on having the time and energy to do so. (Also, I would not be the least bit surprised if somebody else has already done something like this; I’m not Googling for it, because the point is to entertain myself by thinking about how I would use these.)
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And if you would like to share suggestions of cartoon tropes that would work well in this sort of context, the comments will be open.
In the cartoons, the equipment all comes from Acme. In the physics problem sets, it's from the Ideal Hardware store -- massless ropes, frictionless pulleys...
The best part of cartoon physics is WHY it's funny: because it reflects reality in a particular type of funhouse mirror. If you don't have a basic feel for how the world works, then the joke falls flat, and goes "Wheeze, wheeeeze" like an accordion as it walks away.
(I learned more physics concepts (mechanics) from Wile E. Coyote than I ever learned in physics class, just trying to figure out why it was so funny)