Fundamentals: Work done by external force

Work done (W = F d) by external force can be quite misleading. There a two different types , force in the direction of motion or opposite to direction of motion normaly referred to as friction. W(+)will mean there is increase in total energy. If W(-) will mean there is decrease in total energy. If the total energy is KE + PE then W + (KE + PE)i = (KE + PE )f. If work is done against friction , then (KE + PE)i = (KE + PE)f + W