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#1 2015-02-03 12:51:21

SuperLynx
Member
Registered: 2009-06-28
Posts: 335

Surface Area Math Question

I have an object which it's surface Area is 395.2722194 Unit^2.  I want to break this number down into the height, width and depth of the object is this possible ?

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#2 2015-02-03 13:54:26

anonimnystefy
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From: Harlan's World
Registered: 2011-05-23
Posts: 16,049

Re: Surface Area Math Question

No. Without any further information, this object have any shape and size.

Do you know anything else about the object?


“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

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#3 2015-02-03 15:37:08

SuperLynx
Member
Registered: 2009-06-28
Posts: 335

Re: Surface Area Math Question

That is all I know about the object ?

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#4 2015-02-03 15:39:51

classof2020
Member
Registered: 2015-02-03
Posts: 4

Re: Surface Area Math Question

do you know what type of object it is? for example, a cube, rectangular prism, etc. ?

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#5 2015-02-03 16:08:05

SuperLynx
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Registered: 2009-06-28
Posts: 335

Re: Surface Area Math Question

Rectangle !

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#6 2015-02-03 20:50:06

Bob
Administrator
Registered: 2010-06-20
Posts: 10,053

Re: Surface Area Math Question

hi SuperLynx

If the faces are rectangles and the cuboid has dimensions a by b by c then the surface area is

area = 2ab + 2ac + 2bc

There are (infinitely) many  values of a, b and c that will give that value so you cannot specify one unique set of values.

If you choose a and b then you can compute c = (area - 2ab)/(2a + 2b).

Bob


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 smile

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#7 2015-02-04 02:18:58

SuperLynx
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Registered: 2009-06-28
Posts: 335

Re: Surface Area Math Question

Sorry I don't understand ?

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#8 2015-02-04 05:26:28

Bob
Administrator
Registered: 2010-06-20
Posts: 10,053

Re: Surface Area Math Question

FdGAlYn.gif

Bob


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 smile

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#9 2015-02-04 16:39:42

SuperLynx
Member
Registered: 2009-06-28
Posts: 335

Re: Surface Area Math Question

bob bundy wrote:

http://i.imgur.com/FdGAlYn.gif

Bob

What are you telling me, I'm still puzzled ?

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#10 2015-02-04 20:20:40

Bob
Administrator
Registered: 2010-06-20
Posts: 10,053

Re: Surface Area Math Question

If you are seeing the link, you have images turned off.

You can change this in the display section of your profile.

You can also load that image directly from imgur by copying it into your browser.

Bob


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 smile

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#11 2015-02-05 02:32:56

SuperLynx
Member
Registered: 2009-06-28
Posts: 335

Re: Surface Area Math Question

The image loaded, my question is; so you can break down the surface area ^2 into the 6 faces of a rectangle ?

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#12 2015-02-05 07:46:33

Bob
Administrator
Registered: 2010-06-20
Posts: 10,053

Re: Surface Area Math Question

Yes.  That is what they mean by the 'surface area of the cuboid'.

Bob


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 smile

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#13 2015-02-05 14:47:19

SuperLynx
Member
Registered: 2009-06-28
Posts: 335

Re: Surface Area Math Question

What if the surface is not a rectangle, but shape, for example, a car, or a human body ?

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#14 2015-02-05 23:32:56

Bob
Administrator
Registered: 2010-06-20
Posts: 10,053

Re: Surface Area Math Question

Those would be tricky to work out.  There's no easy formula as people and cars have many shapes.

You could estimate by making a square grid and holding it against the surface and counting up squares.  Hard to be accurate though.

There are formulas for some solids: sphere, cone, pyramid etc.

Bob


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 smile

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#15 2015-02-06 01:44:10

SuperLynx
Member
Registered: 2009-06-28
Posts: 335

Re: Surface Area Math Question

bob bundy wrote:

Those would be tricky to work out.  There's no easy formula as people and cars have many shapes.

You could estimate by making a square grid and holding it against the surface and counting up squares.  Hard to be accurate though.

There are formulas for some solids: sphere, cone, pyramid etc.

Bob

What if you pretended as though the car, or person was contained, I believe as you are saying in a solid shape; as in a cube etc, that would work ?

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#16 2015-02-06 07:28:00

Bob
Administrator
Registered: 2010-06-20
Posts: 10,053

Re: Surface Area Math Question

For surface area, it's not as simple as that.  If you wanted the volume of an irregular solid, you could enclose it in a solid you could measure, and that would give you an upper bound.

But it is possible to enclose a solid entirely in a finite solid, and yet have an infinite surface area.  Does that sound weird ?  The 'trick' is to give it lots of nooks and crannies that increase the surface area without increasing the enclosing solid.  Have a look at this:

http://en.wikipedia.org/wiki/Menger_sponge

Bob


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 smile

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#17 2015-02-06 15:48:34

SuperLynx
Member
Registered: 2009-06-28
Posts: 335

Re: Surface Area Math Question

How is the program giving me the values posted in my first message for a irregular solid ?

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#18 2015-02-07 04:17:29

Bob
Administrator
Registered: 2010-06-20
Posts: 10,053

Re: Surface Area Math Question

We have already said that, if it is irregular, then it is not possible to give values.  Indeed what would height width and depth mean if it were irregular?

Bob


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 smile

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#19 2015-02-07 08:10:32

SuperLynx
Member
Registered: 2009-06-28
Posts: 335

Re: Surface Area Math Question

What does the surface Area is 395.2722194 Unit^2 represent for a irregular object ?

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#20 2015-02-08 09:11:34

Bob
Administrator
Registered: 2010-06-20
Posts: 10,053

Re: Surface Area Math Question

Cover the solid in approximate cm squares and count them:

vC1eIA8.gif

Bob


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 smile

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#21 2015-02-08 12:07:11

SuperLynx
Member
Registered: 2009-06-28
Posts: 335

Re: Surface Area Math Question

bob bundy wrote:

Cover the solid in approximate cm squares and count them:

http://i.imgur.com/vC1eIA8.gif

Bob

I don't understand what you mean ?

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#22 2015-02-08 16:05:20

CIV
Member
Registered: 2014-11-09
Posts: 74

Re: Surface Area Math Question

You can not simply derive measurements such as height, width, and depth for a complicated shape such as a human body or car with more data. Even if you had this data, its extremely difficult to do. If your object was simple such as a cube, cylinder, or triangle and had more data,... we could calculate this a lot easier.

Not knowing any more than just the SA of say a box,... we can derive dimensions for say a box but there are infinitely many dimensions. This means the box can be of any shape or even size. If you give us the SA, L, and W, we can calculate the depth for example. If you only give the SA and L, that would mean the width and depth would be infinite.

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#23 2015-02-08 16:20:41

SuperLynx
Member
Registered: 2009-06-28
Posts: 335

Re: Surface Area Math Question

CIV wrote:

You can not simply derive measurements such as height, width, and depth for a complicated shape such as a human body or car with more data. Even if you had this data, its extremely difficult to do. If your object was simple such as a cube, cylinder, or triangle and had more data,... we could calculate this a lot easier.

Not knowing any more than just the SA of say a box,... we can derive dimensions for say a box but there are infinitely many dimensions. This means the box can be of any shape or even size. If you give us the SA, L, and W, we can calculate the depth for example. If you only give the SA and L, that would mean the width and depth would be infinite.

I understand. A program I use only gave me those measurements from a irregular object, the program must be getting the information some how, some way, that is what I want to know ?

We both can agree that the program is not spitting out a random value for the surface area of the object !

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