Did I prove this Bernoulli equation correctly?

In summary, the Bernoulli equation is a fundamental equation in fluid mechanics that relates pressure, velocity, and height of a fluid in motion. It is important because it allows us to understand and predict fluid behavior in various situations. To ensure correct application, all terms should be consistent and applied at two distinct points. The equation makes assumptions about the fluid and flow, and may require modifications in special cases. It does have limitations, such as only being applicable to steady flow and not accounting for energy losses or external forces.
  • #1
Pengwuino
Gold Member
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Given a differential equation with the form:

[tex]\frac{{dy}}{{dx}} + P(x)y = Q(x)y^n [/tex]

and using the substitution [tex]v = y^{1 - n}[/tex]

I attempted to prove that it transforms into

[tex]\frac{{dv}}{{dx}} + (1 - n)P(x)v = (1 - n)Q(x)[/tex]

Here’s the proof, did I do it correctly? I got the write answer so I assume I did :D

[tex]\begin{array}{l}
y = v^{ - 1 + n} \\
\frac{{dv}}{{dx}} = \frac{{dv}}{{dy}}\frac{{dy}}{{dx}} \\
\frac{{dv}}{{dy}} = (1 - n)y^{ - n} \frac{{dy}}{{dx}} \\
\frac{{y^n }}{{(1 - n)}}\frac{{dv}}{{dx}} = \frac{{dy}}{{dx}} \\
\frac{{y^n }}{{(1 - n)}}\frac{{dv}}{{dx}} + P(x)y = Q(x)y^n \\
\frac{{dv}}{{dx}} + (1 - n)P(x)\frac{y}{{y^n }} = (1 - n)Q(x) \\
\frac{{dv}}{{dx}} + (1 - n)P(x)y^{1 - n} = (1 - n)Q(x) \\
\frac{{dv}}{{dx}} + (1 - n)P(x)v = (1 - n)Q(x) \\
\end{array}
[/tex]
 
Last edited:
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  • #2


Yes, your proof is correct! You used the substitution correctly and showed each step clearly. Good job!
 

1. What is the Bernoulli equation and why is it important?

The Bernoulli equation is a fundamental equation in fluid mechanics that relates the pressure, velocity, and height of a fluid in motion. It is important because it allows us to understand and predict the behavior of fluids in various situations, such as in pipes, around objects, or within different types of flow.

2. How do I know if I have applied the Bernoulli equation correctly?

To ensure that the Bernoulli equation has been applied correctly, you should check that all terms in the equation (pressure, velocity, and height) are consistent with the type of flow being analyzed. Additionally, the equation should be applied at two distinct points along the flow path, and the resulting values should be consistent with the expected behavior of the fluid.

3. What are the assumptions made in the Bernoulli equation?

The Bernoulli equation makes several key assumptions, including that the fluid is incompressible, inviscid, and irrotational. It also assumes that the flow is steady and that the fluid properties are constant along the flow path.

4. Can the Bernoulli equation be used for all types of fluid flow?

The Bernoulli equation can be used for most types of fluid flow, as long as the assumptions are met. However, it is not applicable for highly viscous or turbulent flows, and special cases may require modifications to the equation.

5. Are there any limitations to the Bernoulli equation?

While the Bernoulli equation is a powerful tool in fluid mechanics, it does have limitations. It only applies to steady flow situations and does not take into account any energy losses due to friction or other factors. It also does not consider any external forces acting on the fluid, such as gravity or external pressure.

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