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 Posted: Thu Oct 11, 2012 9:02 pm

Joined: Tue Feb 02, 2010 10:07 am
Posts: 64
I have come across terminology in work sheets on shapes that refer to:

Non square rectangle
Non rectangular parallelogram
Non square rhombus

Instead of just rectangle, parallelogram, rhombus.

Are there any primary teachers who could enlighten me as to the reasoning behind creating this terminology (instead of just teaching a square is also a rectangle etc.) and if this is what the children now have to call these shapes?

Thanks

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 Posted: Thu Oct 11, 2012 9:09 pm

Joined: Mon Jun 18, 2007 2:32 pm
Posts: 7140
Location: East Kent
I've not heard of that,( but who knows it may be a new 'initiative'!)

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 Posted: Thu Oct 11, 2012 9:22 pm

Joined: Mon Aug 22, 2011 8:20 pm
Posts: 1706
Location: Warwickshire
I suppose it makes it more obvious that a square is a special case of a rectangle etc.

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 Posted: Wed Oct 31, 2012 2:13 pm

Joined: Tue Jul 21, 2009 9:56 pm
Posts: 8545
Yes - shape teaching seems so delightfully vague, but then children are marked right or wrong if they don't follow the school's version of it e.g. no-one seems to really explain what a prism is until much later on so many teachers will mark it wrong if a cylinder is called a prism, the word rectangle gets misused and treated as though it excludes a square etc etc. I'm never quite sure why all this is taught in KS1. Have you come across a domino as well? We got this in a homework recently - it's a non-square rectangle (!!) (oblong in other words) which if you halve it along the long side results in two squares.

Regular polygons seem to get incorrectly taught as well - a common omission is to forget that the angles are equal, not just the sides.

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 Posted: Wed Oct 31, 2012 3:06 pm

Joined: Thu May 10, 2012 8:30 am
Posts: 247
mystery wrote:
many teachers will mark it wrong if a cylinder is called a prism

And rightly so. Prisms are defined in terms of the congruent polygons that form the ends. There are any number of reasons as to why circles aren't polygons, before we even move on to why the parallelograms that define the faces that join the bases need to have finite sizes.

As a general rule, any argument which attempts to use "infinity" as though it were a natural number generates contradictions by the tonne and fails completely. See "dividing by zero gives infinity" for a common claim which is simply wrong, and which is wrong for reasons related to why circles aren't polygons.

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 Posted: Wed Oct 31, 2012 3:26 pm

Joined: Thu Sep 24, 2009 10:59 am
Posts: 6910
A prism is a polyhedron, which means the cross section will be a polygon (a straight-edged figure) so all sides will be flat.A cylinder is not a prism, because it has curved sides.
Eta you beat me to it daveg, at least I think that is what you were saying.
When I trained to be a teacher back in the eighteenth century, we were told to teach 3D shape before 2D as children would consolidate the relationship between the 2 more easily that way. In practice this was a dismal failure because they all came to school calling spheres 'circles', triangular prisms 'triangles' and cuboids 'squares'.

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 Posted: Wed Oct 31, 2012 4:05 pm

Joined: Thu May 10, 2012 8:30 am
Posts: 247
Amber wrote:
A prism is a polyhedron, which means the cross section will be a polygon (a straight-edged figure) so all sides will be flat.A cylinder is not a prism, because it has curved sides.

That hits the same problem that mystery's definition is prone to: once you make the mistake of thinking that a circle is a polygon, you can use it to argue not only that cylinders are prisms, but also that spheroids are polyhedra, because sections through them are ellipses, which are in turn deemed polygons. The basic misunderstanding is claiming that a circle is a polygon, usually involving some mess with "infinity" which A Level maths isn't quite up to getting you out of. The rest of the misconceptions flow from there.

Quote:
they all came to school calling spheres 'circles', triangular prisms 'triangles' and cuboids 'squares'.

See Flatland.

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 Posted: Wed Oct 31, 2012 4:14 pm

Joined: Thu Sep 24, 2009 10:59 am
Posts: 6910
I'm lost, daveg, you are blinding me with clever things. Second time in a week you are making me look stupid. I shall soon test your knowledge of Pushkin in the original, which you bragged about, because I really can.

I was quoting from teaching notes. I have never needed to know the properties of a 3D shape other than to teach them to others. Likewise I have never needed to tesselate, rotate, conjugate or otherwise manipulate little figures drawn on squared paper.

This reminds me of my favourite ever remark in a school report (accompanied by a rather generous 'D' grade) when I was 12, for technical drawing. 'Amber has shown that she can produce good work, but rarely makes the effort to do so.' I can still visualise that silly anvil thing we had to draw now. Bet you got an 'A'.

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 Posted: Wed Oct 31, 2012 4:19 pm

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 14002
I love Flatland even though it is somewhat s e xist. My wonderful A level maths teacher recommended it to me and I've been happy to lend the book many times since then.

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 Posted: Wed Oct 31, 2012 4:53 pm

Joined: Sun Sep 09, 2012 6:32 pm
Posts: 291

Dare I admit that we have things like this on our wall for fun?!

And when the children were little they put 'tetrahedrons' in the 'triangle' shaped hole on their shape sorters. It was all part of a silly bet as to how old DS was before he said tetrahedron, but he does now love shapes and their properties.

I'll get my coat.

_________________
The more that you read, the more things you will know.
The more that you learn, the more places you'll go.
Dr Seuss

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