Infinitesimal volume using differentials

In summary, infinitesimal volume dV = dx dy dz is used in some texts because it represents the dimensions of a small rectangular solid, with dx, dy, and dz being the changes in the axis variables. This can also be expressed as dV = y z dx + x z dy + x y dz through partial differentiation.
  • #1
girolamo
6
0
Hi, I don't understand why in some texts they put that infinitesimal volume dV = dx dy dz. If V = x y z, infinitesimal volume should be dV = y z dx + x z dy + x y dz, by partial differentiation. Thanks
 
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  • #2
girolamo said:
Hi, I don't understand why in some texts they put that infinitesimal volume dV = dx dy dz.
Because the dimensions of the box are dx, dy, and dz. The volume of this box is dV, which is dx * dy * dz.
girolamo said:
If V = x y z, infinitesimal volume should be dV = y z dx + x z dy + x y dz, by partial differentiation. Thanks

This would be the change in volume of a box whose dimensions are x, y, and z, and whose dimensions change by dx, dy, and dz.
 
  • #3
girolamo said:
Hi, I don't understand why in some texts they put that infinitesimal volume dV = dx dy dz. If V = x y z, infinitesimal volume should be dV = y z dx + x z dy + x y dz, by partial differentiation. Thanks

It's for the same reason that dA = dx*dy.
 
  • #4
dx dy dx dz are three independent small changes in the axis variables. You can think of the as spanning a small rectangular solid.
 

1. What is an infinitesimal volume?

An infinitesimal volume is a very small volume, approaching zero, that is used in mathematical calculations to represent a small change in a variable.

2. How is infinitesimal volume calculated using differentials?

Infinitesimal volume is calculated using differentials by taking the product of the three differentials: dx, dy, and dz. This represents the change in x, y, and z values, respectively, and gives the infinitesimal volume.

3. What is the purpose of using differentials in calculating infinitesimal volume?

Differentials allow for a more accurate and precise calculation of infinitesimal volume. They take into account the small changes in a variable, rather than just using a fixed value, resulting in a more precise answer.

4. Can infinitesimal volume be negative?

Yes, infinitesimal volume can be negative. This occurs when the change in a variable is in the opposite direction than what was initially assumed. However, in most cases, infinitesimal volume is considered to be positive.

5. What are some real-world applications of using infinitesimal volume and differentials?

Infinitesimal volume and differentials are used in many areas of science and engineering, including physics, chemistry, and economics. They are particularly useful in calculating rates of change, such as velocity and acceleration, in dynamic systems. They are also used in optimization problems, such as finding the maximum or minimum value of a function.

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