Math Is Fun Forum

2Bhonest

Member

Registered: 2011-11-28

Posts: 9

Solid Figures

My sons math worksheet says: what rule tells how these solid figures are alike?
Has a picture of a cylinder and a rectangle.........

Any ideas?

Thanks for all your help

Bob

Administrator

Registered: 2010-06-20

Posts: 10,627

Re: Solid Figures

hi 2Bhonest,

Have a look at my picture.

A is a cylinder

C is a rectangle

C is NOT a solid.  It is a flat, two dimensional shape.

B is a cuboid.

That IS a solid.  It is three dimensional.

So is the worksheet showing something like A and B rather than A and C?

I'm going to guess the answer to that is YES.

So what have A and B got in common?

If you take a circle and stretch it up in the air it traces out a cylinder.

If you take a rectangle (or maybe a square) and stretch it up in the air it traces out a cuboid.

So that's what they have in common. 

Bob

Last edited by Bob (2011-12-05 11:48:04)

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

2Bhonest

Member

Registered: 2011-11-28

Posts: 9

Re: Solid Figures

It shows a and b

Bob

Administrator

Registered: 2010-06-20

Posts: 10,627

Re: Solid Figures

Oh hi,

Stay on-line while we sort this out.

Bob

I've edited my other post a bit so have a look and see if what I've said makes sense.

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

2Bhonest

Member

Registered: 2011-11-28

Posts: 9

Re: Solid Figures

Im here now. That just sounds rough for a 1 st grader, don't you think? Or may be I have been out of it for awhile.

Last edited by 2Bhonest (2011-12-05 12:21:34)

Bob

Administrator

Registered: 2010-06-20

Posts: 10,627

Re: Solid Figures

hi 2Bhonest,

Yes, it does sound a tough challenge.

Let's do the math for your benefit first.

Solids like that are called prisms.

The MathsIsFun teach yourself page on prisms has some good, colourful pictures that will help you and him.

http://www.mathsisfun.com/geometry/prisms.html

The properrty that makes a solid into a special one called a prism is that it has the same cross-section along its length.

I've put a picture of a hexagonal prism below.  The shaded bit shows the cross section.

Compare with, for example, a pyramid.

http://www.mathsisfun.com/geometry/pyramids.html

Do you have candy sweets called 'rock' in the US?  In the UK it's popular with kids when on holiday at the seaside.  They make it by making a shape or words with one colour of candy and surrounding it with white candy and a pink border.  Then they stretch it out to make a long stick.  The result is a candy bar that has the picture / words all the way through.  In effect, it's a prism because it has the same cross section.  So UK kids understand prisms because they've eaten one.  (see picture)

So how does that help your son?

Well, I think show him the pages of prisms and then, pyramids; and ask him to put into words what the prisms have in common.  That's why I used the words 'stretched up in the air'.  It was my attempt to get inside the head of a grade one kid.  Probably failed miserably, which is why I suggest asking him to put it into words.  Hopefully, you know the background now, so can nudge him in the right direction.

Hope that helps,

Bob

Last edited by Bob (2011-12-05 21:10:59)

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob