Editing Simple machine (section)

===Proof===
When a machine moves in the forward direction from point 1 to point 2, with the input force doing work on a load force, from conservation of energy<ref name="Rao">{{cite book
  | last1 = Rao
  | first1 = S.
  | first2 = R.
  | last2 = Durgaiah
  | title = Engineering Mechanics
  | publisher = Universities Press
  | year = 2005
  | pages = 82
  | url = https://books.google.com/books?id=vRR4FKAkJl4C&q=%22simple+machine%22+%22&pg=PA80
  | isbn = 978-81-7371-543-3}}</ref><ref name="Goyal">{{cite book
  | last1 = Goyal
  | first1 = M. C.
  | first2 = G. S.
  | last2 = Raghuvanshi
   | title = Engineering Mechanics
  | publisher = PHI Learning Private Ltd.
  | year = 2009
  | location = New Delhi
  | pages = 202
  | url = https://books.google.com/books?id=vRR4FKAkJl4C&pg=PA82
  | isbn = 978-81-203-3789-3}}</ref> the input work <math>W_\text{1,2}</math> is equal to the sum of the work done on the load force <math>W_\text{load}</math> and the work lost to friction <math>W_\text{fric} </math>
{{NumBlk2|:|<math>W_\text{1,2} = W_\text{load} + W_\text{fric}</math>|Eq. 1}}

If the efficiency is below 50% {{nowrap|(<math>\eta = W_\text{load}/W_\text{1,2} < 0.5</math>):}}

<math display="block">2W_\text{load} < W_\text{1,2} \,</math>

From {{EquationNote|Eq. 1}}
<math display="block">\begin{align}
2W_\text{load} & < W_\text{load} + W_\text{fric} \\
W_\text{load} & < W_\text{fric}
\end{align}</math>

When the machine moves backward from point 2 to point 1 with the load force doing work on the input force, the work lost to friction <math>W_\text{fric}</math> is the same

<math display="block">W_\text{load} = W_\text{2,1} + W_\text{fric}</math>

So the output work is
<math display="block">W_\text{2,1} = W_\text{load} - W_\text{fric} < 0</math>

Thus the machine self-locks, because the work dissipated in friction is greater than the work done by the load force moving it backwards even with no input force.