[Bored chemist]

It was Heisenberg's word.

Really?
That's odd. I thought  his work was in German.
http://www.psiquadrat.de/downloads/heisenberg1925.pdf

I think the world has now grown up enough that we could teach physics from quantum mechanics and relativity, pointing out that as we scale up from  atoms and down from near-c velocities, we can make classical approximations, using continuum mathematics and invariant masses for most (but by no means all) engineering purposes.

You propose that we teach physics by starting from something we don't understand or experience and working towards something we do.

I invite you to discuss that ordering  with any teachers you know.

[alancalverd]

I propose to start with something we have known for 100 years, and show how it explains what we see every day. It would need some revision of adjoining subjects, so that the good bits of applied maths (vectors, calculus...) and the classical physics experiments become engineering.

One of my sons is a physics teacher. Unfortunately he is constrained by a curriculum, apparently written by people who consider x-rays "modern". As an Oxford alumnus, you will know that "modern" means "post-Roman" to the cognoscenti. I prefer to call early 20th century physics "knowledge".

[Bored chemist]

I propose to start with something we have known for 100 years

You and I probably have known if for a hundred yeas or so (between us), but we aren't schoolkids.
But trying to teach physics staring with Einstein (F might equal MA) and working back to Newton (F=MA) is just going to confuse the students.

[alancalverd]

It's much easier to paint on a blank canvas.

I'd start with Einstein's discussions about passing trains. How do we know we are moving? We don't!

Then I'd talk about thunderstorms or fireworks: we see the flash long before we hear the bang, and the further away, the bigger the difference, so information travels at different speeds depending on the medium of transmission.

So what do we know about events a long way away? Let's think about history. Time was that information couldn't travel faster than a horse or a ship (how do you organise the Battle of Hastings? One army is loading ships 50 miles away, the other is fighting at Stamford - how do they get to meet?) but even with radio waves (how fast do they travel?) we only know what happened in New Zealand about 0.15 seconds ago.

....and so on. Pretty soon we'll be asking about time dilation.

Then some bright kid will point out that you know when the train starts moving because you can feel the shove and old ladies start falling over, and away we go again....

As soon as you introduce atomic theory you can talk about electrostatics and ask the question (that turns up depressingly often in these boards) why the electron doesn't just stick to the proton like the balloon sticks to the ceiling. You can muck about with cars and stopwatches and investigate the experimental limits of Δv and Δx then skip to Heisenberg's hypothesis that there is a fundamental limit , and away you go with a discussion of indeterminacy that doesn't involve experimental error but does predict the diameter of an atom. 

Now here's a question from an obnoxious schoolkid. How do we know that c is a limit? I can derive Maxwell's equations by a bit of handwaving with a magnet, but why isn't there anything faster, Sir?

Sir Lawrence Bragg (my hero) used to say that you can't claim to understand anything unless  you can explain it to a 7-year-old.  Any takers for this one?

[Bored chemist]

Then some bright kid will point out that you know when the train starts moving because youi cann feel the shove

And that's when Newtonian physics comes in ...

But trying to teach physics staring with Einstein (F might equal MA) and working back to Newton (F=MA) is just going to confuse the students.

[Bored chemist]

It's much easier to paint on a blank canvas.

Exactly; you need the canvas first.

[alancalverd]

Then some bright kid will point out that you know when the train starts moving because youi cann feel the shove

And that's when Newtonian physics comes in ...

Big problem. Newtonian physics ends up with the remarkable finding that gravitational mass = inertial mass, but doesn't explain why.

All you need to move on with the relativity discussion is to note that we can detect acceleration but not constant velocity, which is what the kid has just told you. That finding can take you in both directions but whilst the Einsteinian  formalism degenerates to Newtonian if v<<c, the reverse is not the case, which is why relativity had such a hard time getting accepted until proven by experiment.

[Bored chemist]

All you need to move on with the relativity discussion is to note that we can detect acceleration but not constant velocity,

What we actually "detect" is a force. If the car accelerates forwards, I get "pushed"  back into my seat and (per Newton) I feel the seat push back on me.
At constant velocity A = 0 and thus F=0
So, Newtonian physics explains that just fine.

But you can't explain how we "detect" acceleration without using Newtonian physics.

[alancalverd]

Newtonian physics doesn't explain F = ma, but states it either as a definition of F, an observed fact, or a consequence of F = d(mv)/dt, all of which is true for small v but by no means explained.

All we need to get the relativistic discussion going is the observation that old people fall over when the bus starts or stops, but seem quite capable of standing up when it's cruising at 50 mph. Today's bright kids might wonder why they lock the toilet doors  when a plane enters the approach pattern: again Newton calculates the pee arc, but doesn't explain it, or extend it to explain how GPS works.   

[Bored chemist]

Newton calculates the pee arc, but doesn't explain it, or extend it to explain how GPS works.   

That would be relevant if, and only if, I was saying that we shouldn't teach relativity.
You seem to be planning to start with why the GPS clocks are set to tick at  the wrong rate (here on Earth) and go on from that to explain how a go-cart rolls down a hill.

[alancalverd]

I have no idea why a go-cart rolls down a hill. Nobody knows why gravity only sucks, or why m_inertia = m_gravitation, even though we can calculate how fast it would go on Mars.

Our ancestors knew the sun would rise in the same place every 365.25 days and the spring tide came with a new or full moon, but had no idea why. The observation and empirical calculation made farming and sailing a lot easier, and  Newtonian physics doesn't take us much further.

[Bored chemist]

Nobody knows why gravity only sucks, or why minertia = mgravitation,

Nor do I. Nor did Newton, Nor did Einstein.

Newtonian physics ends up with the remarkable finding that gravitational mass = inertial mass, but doesn't explain why.

So... it's the same as relativistic physics.
Since they are the same (except one is more complicated) why not teach the simpler one first?


If you were building a house, would you try to put the roof on first?

[alancalverd]

Not a house, but I often erect a small marquee for jazz concerts and always start with the roof.

The problem is that if you teach, say, the Bohr atom, you then have to spend hours explaining why it isn't a good model when people make entirely logical but clearly wrong deductions from it. We don't teach humors and miasms, creationism, divination from chicken entrails, or compression waves in the aether (which still turned up in radio engineering texts in the 1930s) so why not proper physics?

If you were brought up on miasms, you might find virology hard to comprehend, but it's part of the A level syllabus because it's what we (except politicians) know to be true.   

[Bored chemist]

We don't teach humors and miasms, creationism, divination from chicken entrails, or compression waves in the aether

False equivalent
None of those is a simplification of the real world which applies in the low velocity (or any analogous) situation, is it?
Why did you bring it up?

but I often erect a small marquee for jazz concerts and always start with the roof.

And then, presumably, you go hunting and foraging for something to hold it up.
Or are there pre arranged poles?
Because, if there are, you don't raise the roof until you have the poles.

[alancalverd]

They are all previously accepted models of reality that don't stand up to rigorous analysis.

Since the real world seems to behave according to relativity and quantum mechanics, with as much rigor as we can apply, surely they should be the foundation on which we base our models?