Math Is Fun Forum

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 ?

anonimnystefy

Real Member

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?

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“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
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SuperLynx

Member

Registered: 2009-06-28

Posts: 335

Re: Surface Area Math Question

That is all I know about the object ?

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. ?

SuperLynx

Member

Registered: 2009-06-28

Posts: 335

Re: Surface Area Math Question

Rectangle !

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

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

SuperLynx

Member

Registered: 2009-06-28

Posts: 335

Re: Surface Area Math Question

Sorry I don't understand ?

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: Surface Area Math Question

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

SuperLynx

Member

Registered: 2009-06-28

Posts: 335

Re: Surface Area Math Question

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

Bob

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

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

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

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 ?

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

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

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 ?

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

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

SuperLynx

Member

Registered: 2009-06-28

Posts: 335

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

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 ?

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

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

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 ?

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

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

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 ?

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: Surface Area Math Question

Cover the solid in approximate cm squares and count them:

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

SuperLynx

Member

Registered: 2009-06-28

Posts: 335

Re: Surface Area Math Question

Cover the solid in approximate cm squares and count them:

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

Bob

I don't understand what you mean ?

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.

SuperLynx

Member

Registered: 2009-06-28

Posts: 335

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.

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 !