Poundal is a unit of force in the pound-foot-second (fps) system, commonly used in English-speaking countries before the adoption of the International System of Units (SI). It is defined as the force required to accelerate a mass of one pound at a rate of one foot per second squared. The unit symbol for the poundal is “pdl”.

One poundal is equivalent to:
- 0.138255 newtons (N)
- 3.108095 dynes (dyn)
Historical Significance of Poundal
The poundal has been used in a wide range of scientific and engineering applications throughout history. It was first introduced by James Clerk Maxwell in 1871 as a more convenient alternative to the pound-force. The pound-force, denoted as “lbf”, is a measure of the gravitational force exerted on a mass of one pound.
The poundal gained popularity in the field of engineering due to its compatibility with the fps system, which was commonly used at the time for various calculations. It was particularly useful in fluid mechanics, where the force of gravity is often expressed in poundals.
Advantages and Disadvantages of Poundal
Advantages:
- Convenience: The poundal is a convenient unit to use in calculations involving force and mass, especially in the fps system.
- Simplicity: The definition of the poundal is straightforward and easy to understand, making it accessible to a wide range of users.
- Compatibility: The poundal is compatible with the fps system, which is still commonly used in some engineering fields.
Disadvantages:
- Incompatibility with SI: The poundal is not part of the SI system, which is the internationally accepted standard for scientific measurements. This can lead to confusion and conversion errors when working with data from different sources.
- Lack of widespread use: The poundal has been largely phased out in favor of the newton in most scientific and engineering applications. As a result, finding resources and information on the poundal can be challenging.
Applications of Poundal
Despite its declining use, the poundal still has some practical applications today, particularly in legacy systems and historical documents. Here are a few examples:
- Fluid mechanics: The poundal is still used in some fluid mechanics calculations, especially in the analysis of flows with low Reynolds numbers.
- Geotechnical engineering: The poundal is occasionally used in geotechnical engineering to calculate the force exerted by soil particles on retaining structures.
- Historical analysis: The poundal is invaluable in analyzing historical documents and data where force measurements were recorded in this unit.
Elasto-Inquiry: An Innovative Application for Poundal
In recent years, a new application for the poundal has emerged in the field of materials science. Elasto-inquiry is a technique that uses the poundal to measure the elastic properties of materials. By applying a known force to a material sample using a poundal-based apparatus, researchers can determine the material’s stiffness, Young’s modulus, and other mechanical characteristics.
Poundal in Tables
Table 1: Conversion Factors for Poundal
Unit | Conversion |
---|---|
Newton (N) | 1 pdl = 0.138255 N |
Dyne (dyn) | 1 pdl = 3.108095 dyn |
Table 2: Common Forces Expressed in Poundals
Force | Value (pdl) |
---|---|
Weight of a 1-pound mass at sea level | 32.174 |
Force required to accelerate a 1-pound mass at 1 ft/s² | 1 |
Force exerted by a 1-pound weight hanging from a string | 32.174 |
Table 3: Poundal Equivalents in Other Units
Unit | Value |
---|---|
Gram-force (gf) | 1 pdl ≈ 453.592 gf |
Kilogram-force (kgf) | 1 pdl ≈ 0.004448 kgf |
Pound-force (lbf) | 1 pdl = 0.031081 lbf |
Table 4: Tips and Tricks for Using Poundal
- Convert to SI: When working with data from different sources, it is essential to convert poundals to SI units (newtons) for consistency.
- Understand the context: In historical documents, the term “poundal” may refer to either the pound-force or the poundal. Determine the correct meaning based on the context.
- Use a conversion calculator: There are numerous online and offline tools available to quickly convert poundals to other units of force.
Common Mistakes to Avoid
- Confusing poundal with pound-force: The poundal and pound-force are distinct units of force. The poundal measures force in the fps system, while the pound-force measures force in the gravitational system.
- Assuming poundal is still widely used: The poundal is no longer commonly used in most scientific and engineering applications. Always check the context to ensure that the unit being used is appropriate.
- Using poundal in high-accuracy measurements: The poundal is not as precise as the newton, especially for high-accuracy measurements. Consider using the newton for these applications.
Conclusion
The poundal has a rich history as a unit of force in the fps system. While its use has declined in favor of the SI unit newton, it still finds applications in legacy systems, historical analysis, and innovative fields such as elast