The force which oppose the relative motion between the two body in contact and acts tangential to the surface is called friction. and there are two types of friction.
1. Advantages of friction :-  safe walking on the floor is possible because of friction. 
ii. friction help the finger to hold the pen or tumbler ..

2.Disadvantages of friction :-  friction  results in power loss in  engines and bring  down their  efficient .
ii. friction generate unnecessary heat in machinery parts which may aster their operating conditions.
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