Page Force In SI the unit of force is the newton N defined as a kgm s In Imperial the unit of force is the pound lb Conversion .8 N . lb Weight In the SI system weight can be calculated from Weight F mg where g .8 m/s In Imperial the mass of an object rarely used) in slugs can be calculated from the known weight in pounds Weight ft m g 2. g s   Belt Drives μθ F F=F e or ln μθ F       Where µ coefficient of friction θ angle of wrap e .71 F force in tight side F force in slack side