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#1 2006-10-31 04:38:50

gravity
Member
Registered: 2005-12-07
Posts: 4

Measuring perimeters

My 8 year old daughter has been told to measure the perimeter of 4 household objects. Surely you can only measure the area of 3D objects? You only measure perimeters when using 2D shapes?

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#2 2006-10-31 04:44:23

Devantè
Real Member
Registered: 2006-07-14
Posts: 6,400

Re: Measuring perimeters

I don't think that is true; You just calculate the perimeter of a 3D object in parts (feel free to correct me if I'm wrong, anybody).

For example, if I had a CD case that had 12 edges, I would add up the lengths of all of those edges to get a final result.

Also, the simple equations used in Primary a lot are;

A = LW
V = LWH

And the perimeter is just the distance around the object.

But I haven't studied this in a long time, so I am weary of it.

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#3 2006-10-31 09:10:24

MathsIsFun
Administrator
Registered: 2005-01-21
Posts: 7,711

Re: Measuring perimeters

Perimeter is a 2D concept.

Perhaps the teacher wants you to imagine an object as being 2D ... such as a table top or saucer.

Alternatively you could look at the cross section of a 3D object, which would be 2D. In this way you could get the perimeter of, for example, your waist.


"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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#4 2006-10-31 09:28:45

Devantè
Real Member
Registered: 2006-07-14
Posts: 6,400

Re: Measuring perimeters

I think you could also treat a perimeter as a 3D concept;

The perimeter is the distance around an object. So, the distance around a 3D object is just the same as calculating the perimeter as if it were 2D.

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#5 2006-10-31 09:57:44

polylog
Member
Registered: 2006-09-28
Posts: 162

Re: Measuring perimeters

But what about a cone -- the distance around the tip is 0 (from the side view), the distance around the base is something else, the distance around a side is different .. there are an infinite number of choices!

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#6 2006-10-31 10:06:17

luca-deltodesco
Member
Registered: 2006-05-05
Posts: 1,470

Re: Measuring perimeters

for a 3d object, perimeter is not defined, but if you really wanted to call it something, it would be its surface area.

MathsIsFun wrote:

Perhaps the teacher wants your daughter to imagine an object as being 2D ... such as a table top or saucer.

i agree.

Last edited by luca-deltodesco (2006-10-31 10:07:30)


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#7 2006-10-31 10:27:12

Patrick
Real Member
Registered: 2006-02-24
Posts: 1,005

Re: Measuring perimeters

wikipedia wrote:

The perimeter is the distance around a given two-dimensional object. The word perimeter is a Greek root meaning measure around, or literally "around measure."

I agree with luca-deltodesco and Rod


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