Poundal (pdl)
The poundal (pdl) is a unit of force in the foot-pound-second (FPS) system of measurement. It is defined as the force required to accelerate a one-pound mass by one foot per second squared. In other words,
1 poundal = 1 lb × 1 ft/s².
The poundal is much smaller than the more commonly used pound-force (lbf). It’s mainly used in some engineering contexts and classical mechanics problems where the FPS system is preferred. However, it is less common than the SI unit of force, the newton.
Conversion:
1 poundal ≈ 0.13825 newtons.
Slug
The slug is a unit of mass used primarily in the U.S. customary system and British engineering contexts.
1 slug = 32.174 pounds (lb) (mass)
Equivalent to approximately 14.5939 kilograms (kg)
Defined so that when a force of one pound-force (lbf) acts on a mass of one slug, it accelerates at 1 ft/s² (using F=ma in imperial units).
Key Facts:
Used mainly in physics and engineering for calculations involving Newton’s second law in imperial units
Allows consistent use of pound-force and pound-mass without extra conversion factors
Useful in dynamics, ballistics, and engineering mechanics
The slug bridges the gap between force and mass in the imperial system, making calculations easier when using pound-force units.