In this system, the base unit of length is the foot (ft), and the base unit of time is the second (s). The base unit of force is called the pound-force (lbf), and mass is measured units of slugs, wher...In this system, the base unit of length is the foot (ft), and the base unit of time is the second (s). The base unit of force is called the pound-force (lbf), and mass is measured units of slugs, where 1 slug has a weight of 32.17404855 lbf. At the surface of the Earth, a mass of 1 lbm has a weight of 1 lbf, so sometimes the two are loosely used interchangeably and called the pound (lb), as we do every day when we speak of weights in pounds.
