Monday, 14 November 2011

The Chopped Cubes

We'd done a lesson or two on volume/surface area of a cube & cuboid.

We began Monday showing the kids this wicked GIF of a dude/dudette slicing a large cube:

We chatted about how to create it (some were familiar with online stop-motion software that i'd never heard of!) before one of them asked the question i'd missed:

"It doesn't work though, does it?"

I asked what he meant, and he just said simply that the guy/guyette ends up with 9 little cubes, but you couldn't stick them back into the original shape.

Why? (I said as i face-palmed, having intended to ask them a question about the surface area that would be near impossible for them to answer... *)

He said you could put them in a square, but not 3D unless they were all different sizes, but they seemed the same size.

A couple of the kids spotted that 9 isn't a cube number - we'd need to get rid of one little cube, or get another boatload from somewhere.

One suggested we could make a video that made mathematical sense, i thought this was a great idea and scrapped my lesson.

The kids split into teams and used card to draw nets and build themselves big and small cubes.
One team even went to the trouble of having stages of increasingly small shapes (eg actual size after 1 cut, them after 2 cuts etc) whereas most just went for 1 big cube, and 8 small ones.

We plan to upload and create our own GIFs tomorrow, will post the results when we get done.

Really excited me this one, cos it hits loads of maths, is pretty creative, and came entirely from the kids.

*I was going to ask how much larger the total surface area of all the small cubes was compared to the large cube - could they answer this or am i just being thick?!