Reversible and irreversible Machine

A Machine is said to be a reversible machine, if it is capable of doing the work in reverse  direction, when the effort, causing to lift load is removed,

If the load does not move in reverse direction when the effort it removed, then the machine is called irreversible machine or self – locking machine.

Condition for self locking :

When the effort is removed, self – locking machine will not work in the reverse direction . The necessary condition for this is that the output (W.x) is less than  the frictional work (P.y.  – W.x.)

Therefore, for the machine to be self – locking

(P.y  – W.x.) > W. x

Py > 2 W.x

But          

Thus the condition for self locking is that its efficiency should be less than 50% if the efficiency is more than 50% the machine is reversible.