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Poiseuille's Law gives the rate of flow, \(R,\) of a gas through a cylindrical pipe in terms of the radius of the pipe, \(r,\) for a fixed drop in pressure between the two ends of the pipe. (a) Find a formula for Poiseuille's Law, given that the rate of flow is proportional to the fourth power of the radius. (b) If \(R=400 \mathrm{~cm}^{3} / \mathrm{sec}\) in a pipe of radius \(3 \mathrm{~cm}\) for a certain gas, find a formula for the rate of flow of that gas through a pipe of radius \(r \mathrm{~cm}\). (c) What is the rate of flow of the gas in part (b) through a pipe with a \(5 \mathrm{~cm}\) radius?

Short Answer

Expert verified
Answer: The rate of flow of this gas through a pipe with a 5 cm radius is approximately 3087.5 cm³/sec.

Step by step solution

01

Derive Poiseuille's Law formula

Since the rate of flow, R, is proportional to the fourth power of the radius, r, we can express this relationship as: \[ R = k \times r^4 \] Where \(k\) is the constant of proportionality.
02

Find the constant of proportionality

We are provided the information that the rate of flow, R, is 400 cm³/sec when the pipe radius, r, is 3 cm. Substitute these values into the equation to find the constant of proportionality, k: \[ 400 = k \times (3)^4 \] Solve for k: \[ k = \frac{400}{(3)^4} \] Calculating the value of k: \[ k = \frac{400}{81} \approx 4.94 \]
03

Find the formula for the rate of flow for this gas

Now that we have the value of k, we can substitute it back into our formula to find the equation for the rate of flow of the gas through a pipe with radius r cm: \[ R = 4.94 \times r^4 \]
04

Find the rate of flow for a pipe with a 5 cm radius

To find the rate of flow of this gas through a pipe with a 5 cm radius, substitute the value of r (5) into the equation: \[ R = 4.94 \times (5)^4 \] Calculating the result: \[ R = 4.94 \times 625 \approx 3087.5 \] The rate of flow of this gas through a pipe with a 5 cm radius is approximately 3087.5 cm³/sec.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Rate of Flow
The concept of rate of flow describes how much gas or liquid passes through a pipe per unit of time. In Poiseuille's Law, this is depicted by the variable \( R \), representing the volume flow rate. When you think of rate of flow, imagine how quickly water flows through a garden hose.

In Poiseuille's Law, the rate of flow is crucial because it shows how different factors, like the radius of the pipe, affect this flow. The bigger the radius, the higher the rate of flow, if all else remains constant. It's a direct indicator of how effective a pipe is at transporting fluids.

Understanding the rate of flow helps in various applications, from medical equipment to large-scale pipelines. Knowing how to manipulate it can optimize efficiency and functionality in numerous systems.
Proportionality Constant
A proportionality constant is a fixed number that relates two variables that are proportional. In Poiseuille’s Law, this constant is represented by \( k \). It ties together the rate of flow (\( R \)) and the pipe’s radius (\( r \)) raised to the fourth power.

This means the rate of flow is directly related to \( r^4 \), multiplied by this constant \( k \). The formula looks like this: \( R = k \times r^4 \). The proportionality constant provides a specific value to the theoretical relationship, allowing us to calculate the exact rate of flow for particular conditions.

Once you have specific values, you can calculate \( k \) by rearranging the known relationship. Solving for \( k \) when given \( R \) and \( r \) allows for practical use of Poiseuille's Law in real-world situations.
Cylindrical Pipe
A cylindrical pipe is a tube-shaped structure used to direct fluids from one place to another. It's central to Poiseuille’s Law because the law describes fluid flow through such pipes.

Imagine the pipe as a straight cylinder with a consistent width, known as the radius. This uniform shape makes it easy to apply mathematical equations like Poiseuille's Law to calculate things like flow rate.

The geometric simplicity of a cylindrical pipe ensures that the fluid flow can be calculated accurately, making it ideal for many industrial and everyday applications. Understanding this structure is key to applying Poiseuille’s Law effectively.
Radius Calculation
The radius of a pipe is crucial in determining the rate of flow according to Poiseuille's Law. It is the distance from the center of the pipe to its inner wall, usually measured in centimeters or inches.

When applying Poiseuille's Law, we use the radius to the fourth power, known as \( r^4 \), in the formula \( R = k \times r^4 \). This fourth power relationship means that even a small change in the radius can lead to a significant change in the rate of flow.

Calculating the radius accurately is essential when designing systems that rely on precise fluid dynamics. Ensuring the right radius measurement allows for the correct application of the formula and accurate predictions of flow rate adjustments. Whether in small lab tubing or large pipeline constructions, getting this calculation right is vital for efficiency and performance.

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