Actually, pounds is an acceptable unit for force and mass. One must just specify which kind. For some reason, people don't like using slugs, so the imperial system came up with a conversion factor (gc=32(lbf sec2)/(lbm ft) don't quote me on the units, though) to mess up all of the equations so we can use lbf instead of lbm. On earth(at sea level), 1lbm weighs 1lbf. For example: [math]F_g=G\frac{mM}{{g_c}r^2}[/math] instead of [math]F_g=G\frac{mM}{r^2}[/math] and [math]KE=\frac{m|v|^2}{2g_c}[/math] instead of [math]KE=\frac{m|v|^2}{2}[/math]
That's a good bet since it's not really used anymore. My Physics instructor at NNTPC didn't even know what a slug is.