How Can I Determine the Minimum Volume of a Cube Given the Surface Area?

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Discussion Overview

The discussion revolves around determining the minimum volume of a cube given a fixed surface area. Participants explore the implications of mathematical optimization techniques, particularly in relation to finding extremal values (maximum or minimum) through derivatives, while questioning the existence of a minimum volume under the constraints provided.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that finding dimensions for maximum volume involves taking derivatives and checking for local extrema, but questions how to approach finding minimum volume.
  • Another participant asserts that there is no minimum volume for a box with a given surface area, indicating that the volume can approach zero but not be negative.
  • Some participants discuss the concept of physical boxes, noting that while volume cannot be negative, actual physical constraints (positive dimensions) prevent achieving a volume of zero.
  • One participant challenges the idea of a box with zero volume and finite surface area, seeking clarification on how to find a physical minimum volume.
  • A later reply humorously suggests a box with one dimension being zero, prompting further questions about the nature of such a box.
  • Another participant clarifies that while a "physical" box cannot have zero volume, it can be made arbitrarily small in volume with very small dimensions.
  • One participant reiterates the original question about finding minimum volume, suggesting that assigning a constant volume when surface area is fixed complicates the search for a maximum.

Areas of Agreement / Disagreement

Participants express disagreement regarding the existence of a minimum volume for a cube with a fixed surface area. Some argue that a minimum volume cannot exist under these conditions, while others maintain that physical constraints imply a minimum volume greater than zero.

Contextual Notes

Participants discuss the implications of mathematical optimization and physical constraints, highlighting the dependency on definitions of volume and surface area. The conversation includes unresolved questions about boundary conditions and the nature of extremal values in this context.

Who May Find This Useful

This discussion may be of interest to students and professionals in mathematics, physics, and engineering, particularly those exploring optimization problems and geometric constraints.

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Suppose you are given a problem to find the dimensions for the maximum volume of a cube given the surface area. These problems involve 2 equations, taking the derivative and setting it equal to zero (local minimum or maximum) and substituting the 2nd equation to find the parameters. However, suppose I wanted to know the dimensions with the minimum volume, how can I go about doing that? Clearly using the same method will result in a maximum? When doing these, since setting a derivative to zero gives a local max or min, how is one to know which one will be found?
 
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There is no minimum - or 0, if you like. In principle, setting the derivative to 0 gives all extremal values. If the system has a proper minimum, it will show up there. Otherwise, you can check the boundary conditions of your problem (here: side length > 0).
 
Your saying for a box with a given surface area, it wouldn't have a minimum value for its volume?
 
Woopydalan said:
Your saying for a box with a given surface area, it wouldn't have a minimum value for its volume?
The volume can't go below 0, so that is effectively a minimum value. If you restrict your attention to actual, physical boxes for which all dimensions are positive, you can't get to a volume of 0.
 
Ok if you are given that the surface area has a value that it cannot deviate from, I'm wondering how you guys are proposing a box of zero volume and finite surface area. I know there is a physical minimum volume for a given surface area, how do I go about finding it?
 
Make a box 1 inch long, 1 inch wide, and 0 inches deep.

Volume = 0, surface area = 2. The box still has a finite sized top and bottom, even though you can't put anything inside it.
 
what would a box like this look like? Are you talking about a square?
 
It is like a square, indeed. If you want a "physical" box (with positive side lengths), there is no minimum, but you can make it as close to 0 as you like with an extremely tiny depth.
 
Woopydalan said:
Suppose you are given a problem to find the dimensions for the maximum volume of a cube given the surface area. These problems involve 2 equations, taking the derivative and setting it equal to zero (local minimum or maximum) and substituting the 2nd equation to find the parameters. However, suppose I wanted to know the dimensions with the minimum volume, how can I go about doing that? Clearly using the same method will result in a maximum? When doing these, since setting a derivative to zero gives a local max or min, how is one to know which one will be found?

You already set the volume at a constant when you assigned the surface area. You cannot find a maximum.
 

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