What is the Difference Between Lbf and Lbs?

The difference between "lbf" and "lbs" lies in the units they represent. "Lbf" (pound-force) is a unit of force, while "lbs" (pound) is a unit of mass in the imperial system of units.

• Lbf (Pound-Force): This is the force needed to accelerate a 1 slug mass (32.17405 lbm) at the rate of 1 ft/s². It is used in derived units such as pound-feet, which is the unit of work in the foot-pound-second (f.p.s) system.
• Lbs (Pound): This is a unit of mass in the imperial system (or f.p.s) system of units and is equal to 0.45359237. The pound is used as a basic unit in the feet-pound-second system.

Although "lbs" and "lbf" are related and often confused, they represent different quantities. Lbf refers to the gravitational force placed by a matter on the Earth's surface, while lbs deals with the measurement of force on a matter. In other words, lbf is a force that you would measure with a spring scale, while lbs is a unit of mass that you would measure with a balance.

Comparative Table: Lbf vs Lbs

The difference between "lbf" and "lbs" lies in the fact that "lbf" specifically measures force, while "lbs" measures mass or weight. To differentiate between the two, consider the following table:

In the SI (metric) system of units, kilograms are used for mass, and newtons for weight. In the US system, pounds are used for both mass and weight, which can lead to confusion. To convert lbs to lbf, you can use the following formula:

$$ \text{Force (lbf)} = \text{Mass (lbs)} \times \text{Gravitational Constant} / 9.80665 \times (1 - \frac{\text{Air Density}}{D}) $$

Where M = mass of weight in lbs, g = gravitational constant at fixed location in m/s², d = air density in g/cm³, and D = material density g/cm³.