Comparison with Experimental Results

Oct 13, 2025 by pynkocean.com 17 views

Introduction

In the field of fluid dynamics and rotational dynamics, understanding the forces acting on rotating objects is crucial for designing efficient systems. One such force is drag, which can significantly impact the performance of rotating components. In this article, we will explore the model of drag on a rotating bar about its edge, a concept that has been observed in various applications, including the video "Stuff Made Here" on YouTube, where a rotating beam-like member was found to be slowing down a motor significantly.

Background

Drag is a force that opposes the motion of an object through a fluid, such as air or water. It is caused by the interaction between the fluid and the object, resulting in a resistance to motion. In the case of a rotating bar, the drag force is particularly significant due to the high velocities involved. The drag force can be calculated using various models, including the drag equation, which is a fundamental concept in fluid dynamics.

The Drag Equation

The drag equation is a mathematical formula that calculates the drag force (F_d) acting on an object. It is given by:

F_d = ½ ρ v^2 C_d A

where:

ρ is the density of the fluid (air or water)
v is the velocity of the object
C_d is the drag coefficient, which depends on the shape and size of the object
A is the cross-sectional area of the object

Rotating Bar Model

In the case of a rotating bar, the drag force can be modeled using a similar approach. However, the bar's rotation introduces additional complexities, such as the changing velocity and direction of the fluid flow around the bar. To simplify the problem, we can assume a steady-state flow and a constant velocity around the bar.

Assumptions

For the purpose of this analysis, we will make the following assumptions:

The bar is rotating about its edge, with a constant angular velocity (ω)
The fluid flow around the bar is steady-state and incompressible
The drag coefficient (C_d) is constant and depends only on the shape and size of the bar
The bar is a long, thin cylinder with a circular cross-section

Drag Force Calculation

Using the drag equation, we can calculate the drag force (F_d) acting on the rotating bar. Since the bar is rotating about its edge, the velocity (v) of the fluid flow around the bar is given by:

v = ω r

where r is the radius of the bar.

Substituting this expression into the drag equation, we get:

F_d = ½ ρ (ω r)^2 C_d A

Simplifying the expression, we get:

F_d = ½ ρ ω^2 r^2 C_d A

Discussion

The calculated drag force (F_d) depends on several factors, including the density of the fluid (ρ), the angular velocity (ω) of the bar, the radius (r) of the bar, the drag coefficient (C_d), and the cross-sectional area (A) of the bar. The drag force is proportional to the square of the angular velocity, indicating that even small changes in the bar's rotation rate can result in significant changes in the drag force.

Comparison with Experimental Results

The calculated drag force can be compared with experimental results from the "Stuff Made Here" video on YouTube. In the video, a rotating beam-like member was found to be slowing down a motor significantly. While the exact experimental setup and conditions are not provided, the calculated drag force can be used to estimate the magnitude of the drag force acting on the rotating bar.

Conclusion

In conclusion, the model of drag on a rotating bar about its edge is a complex problem that involves the interaction between the fluid and the rotating object. Using the drag equation and simplifying assumptions, we can calculate the drag force acting on the bar. The calculated drag force depends on several factors, including the density of the fluid, the angular velocity of the bar, the radius of the bar, the drag coefficient, and the cross-sectional area of the bar. The results can be compared with experimental results from the "Stuff Made Here" video on YouTube, providing valuable insights into the behavior of rotating components in fluid dynamics.

Future Work

Future work can focus on refining the model by incorporating additional complexities, such as non-steady-state flow and non-constant drag coefficient. Additionally, experimental studies can be conducted to validate the calculated drag force and provide more accurate estimates of the drag force acting on rotating components.

References

[1] "Drag Equation" by Wikipedia
[2] "Fluid Dynamics" by Cengel, Yunus A.
[3] "Rotational Dynamics" by Kleppner, Daniel, and Robert J. Kolenkow

Appendix

The following appendix provides additional information and derivations used in the calculation of the drag force.

A.1 Derivation of the Drag Force

The drag force (F_d) can be calculated using the drag equation:

F_d = ½ ρ v^2 C_d A

Substituting the expression for the velocity (v) of the fluid flow around the bar, we get:

F_d = ½ ρ (ω r)^2 C_d A

Simplifying the expression, we get:

F_d = ½ ρ ω^2 r^2 C_d A

A.2 Assumptions

For the purpose of this analysis, we made the following assumptions:

The bar is rotating about its edge, with a constant angular velocity (ω)
The fluid flow around the bar is steady-state and incompressible
The drag coefficient (C_d) is constant and depends only on the shape and size of the bar
The bar is a long, thin cylinder with a circular cross-section

A.3 Comparison with Experimental Results

Frequently Asked Questions

In this Q&A article, we will address some of the most common questions related to the model of drag on a rotating bar about its edge.

Q: What is the drag force on a rotating bar?

A: The drag force on a rotating bar is a force that opposes the motion of the bar through a fluid, such as air or water. It is caused by the interaction between the fluid and the bar, resulting in a resistance to motion.

Q: How is the drag force calculated?

A: The drag force can be calculated using the drag equation, which is a fundamental concept in fluid dynamics. The drag equation is given by:

F_d = ½ ρ v^2 C_d A

where:

ρ is the density of the fluid (air or water)
v is the velocity of the fluid flow around the bar
C_d is the drag coefficient, which depends on the shape and size of the bar
A is the cross-sectional area of the bar

Q: What are the assumptions made in the calculation of the drag force?

A: For the purpose of this analysis, we made the following assumptions:

The bar is rotating about its edge, with a constant angular velocity (ω)
The fluid flow around the bar is steady-state and incompressible
The drag coefficient (C_d) is constant and depends only on the shape and size of the bar
The bar is a long, thin cylinder with a circular cross-section

Q: How does the drag force depend on the angular velocity of the bar?

A: The drag force is proportional to the square of the angular velocity (ω) of the bar. This means that even small changes in the bar's rotation rate can result in significant changes in the drag force.

Q: Can the drag force be compared with experimental results?

A: Yes, the calculated drag force can be compared with experimental results from the "Stuff Made Here" video on YouTube. In the video, a rotating beam-like member was found to be slowing down a motor significantly. While the exact experimental setup and conditions are not provided, the calculated drag force can be used to estimate the magnitude of the drag force acting on the rotating bar.

Q: What are the limitations of the model?

A: The model assumes a steady-state flow and a constant drag coefficient, which may not be accurate in all situations. Additionally, the model does not take into account non-constant drag coefficient, non-steady-state flow, and other complexities that may be present in real-world scenarios.

Q: What are the applications of the model?

A: The model can be applied to a wide range of applications, including:

Designing efficient rotating systems, such as wind turbines and propellers
Optimizing the performance of rotating components, such as gears and bearings
Understanding the behavior of rotating objects in fluid dynamics

Q: What are the future directions of research?

A: Future research can focus on refining the model by incorporating additional complexities, such as non-steady-state flow and non-constant drag coefficient. Additionally, experimental studies can be conducted to validate the calculated drag force and provide more accurate estimates of the drag force acting on rotating components.

Conclusion

In conclusion, the model of drag on a rotating bar about its edge is a complex problem that involves the interaction between the fluid and the rotating object. By understanding the drag force and its dependencies, we can design more efficient rotating systems and optimize the performance of rotating components.