Poundal (pdl) - Unit Information & Conversion
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What is a Poundal?
The poundal is an imperial absolute unit of force equal to the force needed to accelerate one pound of mass at one foot per second squared (1 lb⋅ft/s²). Equal to 0.138255 newtons, it is rarely used today but appears in older engineering texts.
History of the Poundal
Introduced in 1879 as part of the foot-pound-second (FPS) absolute system to provide a consistent imperial force unit like the dyne in CGS. Largely obsolete, replaced by pound-force in practical applications and newtons in scientific contexts.
Quick Answer
What is a Poundal? A poundal (pdl) is an absolute imperial unit of force equal to 1 lb⋅ft/s². It represents the force to accelerate 1 pound of mass at 1 ft/s². One poundal = 0.138255 newtons = about 0.031 pounds-force. Historically used in physics calculations with FPS units, now largely obsolete. Appears in older engineering textbooks and historical scientific papers. Use our force converter to convert poundals to newtons, pounds-force, and other units instantly.
Quick Comparison Table
| Poundals | Newtons | Pounds-force | Context | Convert Now |
|---|---|---|---|---|
| 1 | 0.138 | 0.031 | Minimal force | pdl to N → |
| 10 | 1.38 | 0.31 | Light push | pdl to N → |
| 32.2 | 4.45 | 1 | 1 pound-force | pdl to lbf → |
| 100 | 13.8 | 3.1 | Moderate force | pdl to N → |
| 322 | 44.5 | 10 | Strong push | pdl to lbf → |
| 1,000 | 138 | 31 | Heavy force | pdl to N → |
Definition
The poundal (pdl) is the force to accelerate 1 pound mass at 1 ft/s². It is an absolute unit in the FPS system.
Formula: F = ma where F is in poundals, m in pounds, a in ft/s²
Conversions:
- 1 pdl = 0.138255 N (newtons)
- 1 pdl = 0.031081 lbf (pound-force)
- 1 pdl = 14.098 gf (gram-force)
- 1 pdl = 0.014098 kgf (kilogram-force)
- 1 pdl = 138,255 dynes
- 32.174 pdl = 1 lbf
History
The poundal was introduced in 1879 by the British Association for the Advancement of Science as part of the foot-pound-second (FPS) absolute system of units. It was designed to provide a consistent force unit for physics calculations using imperial measurements, analogous to the dyne in the CGS system. The name "poundal" was created from "pound" plus the suffix "-al" to indicate it was an absolute unit rather than a gravitational unit. Despite official endorsement, the poundal never achieved widespread practical use because engineers preferred the more intuitive pound-force. By the mid-20th century, it had become largely obsolete, appearing primarily in older physics textbooks and historical engineering documents.
Common Uses
Historical Physics Textbooks: Pre-1960s physics education using FPS units.
Engineering History: Older technical papers and engineering calculations.
Academic Study: Understanding historical unit systems and conversions.
Specialized Applications: Rare modern use in contexts maintaining FPS absolute units.
Real-World Examples
Comparison to Familiar Forces:
- 1 poundal ≈ force of gentle breath
- 10 poundals ≈ light finger push
- 32.2 poundals = 1 pound-force (weight of 1 lb mass)
- 100 poundals ≈ 3.1 pounds-force
- 322 poundals = 10 pounds-force
- 686 poundals ≈ weight of 70 kg person
Why Poundals Are Confusing: The poundal creates confusion because:
- 1 pound of mass weighs 32.2 poundals (not 1 poundal)
- Unlike pound-force where 1 lb mass = 1 lbf on Earth
- The conversion factor (32.2) is Earth's gravity in ft/s²
Historical Context: In older physics problems:
- "Apply 100 poundals" meant F = ma calculation
- "100 pounds of force" meant weight/gravitational force
- Engineers preferred pound-force; physicists sometimes used poundals
Why It Failed:
- Non-intuitive: 1 lb mass doesn't weigh 1 pdl
- Pound-force more practical for engineering
- Metric system (newton) became international standard
- Created more confusion than it solved
Poundal Conversion Formulas
To Newton:
To Millinewton:
To Kilonewton:
To Meganewton:
To Dyne:
To Pound-force:
To Kilogram-force:
To Gram-force:
To Metric Ton-force:
To US Ton-force:
To UK Ton-force:
To Ounce-force:
To Kip:
Frequently Asked Questions
Formula: N = pdl × 0.138255 Examples:
- 1 pdl = 0.138 N
- 10 pdl = 1.38 N
- 32.2 pdl = 4.45 N (1 lbf)
- 100 pdl = 13.8 N Quick approximation: Multiply by 0.14 for rough conversion. Poundals to Newtons converter →
Convert Poundal
Need to convert Poundal to other force units? Use our conversion tool.