Use of ROTOR present on the Tail of helicopter(An awesome example of Angular Momentum)

Helicopter p.c.:-Google 

Helicopters have a tail rotor or a second main rotor spinning in opposite direction(e.g. Chinook Helicopter) because otherwise along with the primary rotor the body would counterrotate with the primary rotor to give a

 total angular momentum = 0. 

This is the reason when u take a toy helicopter with no tail rotor then u will observe that when u fly that helicopter up then along with its flight the body of the helicopter also counters rotate w.r.t. the primary rotor to nullify the total angular momentum. But the presence of a tail rotor, the thrust produced by tail rotor compensates for the rotation of the body in the opposite direction(torque). As shown in the above diagram