Before revision: The mechanical advantage of a compound machine is the ratio of the output force exerted by the last machine in the series divided by the input force applied to the first machine, that is Because the output force of each machine is the input of the next, , this mechanical advantage is also given by Thus, the mechanical advantage of the compound machine is equal to the product of the mechanical advantages of the series of simple machines that form it Similarly, the efficiency of a compound machine is also the product of the efficiencies of the series of simple machines that form it Self-locking machines The screw's self-locking property is the reason for its wide use in threaded fasteners like bolts and wood screws In many simple machines, if the load force Fout on the machine is high enough in relation to the input force Fin , the machine will move backwards, with the load force doing work on the input force.
After revision: The mechanical advantage of a compound machine is the ratio of the output force exerted by the last machine in the series divided by the input force applied to the first machine, that is Because the output force of each machine is the input of the next, , this mechanical advantage is also given by Thus, the mechanical advantage of the compound machine is equal to the product of the mechanical advantages of the series of simple machines that form it Similarly, the efficiency of a compound machine is also the product of the efficiencies of the series of simple machines that form it Self-locking machines The screw's self-locking property is the reason for its wide use in threaded fasteners like bolts and wood screws In many simple machines, if the load force on the machine is high enough in relation to the input force , the machine will move backwards, with the load force doing work on the input force.