Every night nowadays Barney has taken to hassling me to teach him some new maths. This might seem slightly odd, but when you're six and you've hit upon a game that stops dad from making you go to sleep, you think you're winning...

[Barney will read this in 10 years time, and get very grumpy with me]

We're on spatial symmetry at the moment - we've done the line, plane and rotational flavours thus far, testing ourselves on various objects in the room such as the slightly tricksy four-legged stool and the various button/logo combos on the remote control.

I'm trying to teach Barney & Rosa *proper* applied science - trying to expain with *what's right*, even if it's really mad and hard, and only then moving to the easier approximations.

Newton was wrong, see. Einstein did for him. Why teach stuff that we know is wrong? Much better to try to teach what is right (or rather, most right thus far) and then explain that there are some nice short-cut ways of getting so-close-it-normally-doesn't-matter to the answer.

Similarly, I remember being livid when I realised that the interior angles of a triangle do not *always* add up to 180 degrees.

Next week, I think we'll try differentiation, starting with TGVs...

(and you think I'd joking...)