3D Shapes (lower KS2)

[MutteringDarkly]

DD has some work to do counting edges, surfaces and vertices. How many vertices does a cone have? I get (I think) that it's a point where 2 edges join. One of the worksheets we've been given says the answer for a cone is "0" and another worksheet says it's "1".

I can sort of see the reasoning for both - it has one pointy thing that looks like a corner, but nothing actually joins there...can anyone help?!

[Rudolphian]

I've always been taught it is 1

[tangycalligrapher]

One.

[tangycalligrapher]

www.bbc.co.uk/bitesize/topics/zjv39j6/articles/zcsjqty

[MutteringDarkly]

Thanks both! That makes sense to me, I'm going to stop over-thinking it and ignore the worksheet that says zero

[bettsbattenburg]

0 because the vertices are where the corners meet and a cone has no corners.

[MutteringDarkly]

Noooo I was so close to feeling like I understood!

[bettsbattenburg]

@MutteringDarkly

Noooo I was so close to feeling like I understood!

Ok, look at a 🎲, where each of the edges meet is a vertex. If you look at a cone it has a point at the top but it only has a curved flat face, it doesn't have any edges which meet to form a corner. No edges making a corner means no vertices.

The cone has two faces, one flat and one curved,it has one edge where the flat face meets the curved face but at the top it's not an edge of a face meeting the edge of another face so there cannot be a vertex since a vertex is where two edges meet.

The top of a cone is simply the point at which the curved face has narrowed so it meets, it might make more sense if you roll a piece of card or paper to make a cone but more fun to get a pointy ice cream and have a look, obviously dispose of the contents by whatever means you see fit first you'll understand it better if you do the Ice cream cone test more than once....

[MutteringDarkly]

That's a really helpful explanation, thank you

I am imagining it as flattened piece of paper that would then be rolled into a cone. The flattened piece would have a vertex wouldn't it, where the two long sides of the cone meet at the point?

[bettsbattenburg]

No, they don't form a corner like on a dice so it's not a vertex.

[JustRichmal]

I would have said infinite. The base is a circle with infinite edges, therefore there must be infinite vertices. By the same argument, the pointed part has infinite faces.

To explain this, Imagine a tetrahedron. It has 4 vertices.
A square based pyramid has 5.
A shape with a pentagon at the base will have 6.
One with a decagon at the base will have 11.
A base of 1000 will have 1001.

Each shape is getting closer to the shape of a cone.