Conservation of Angular Momentum Demonstration

 

The student is sitting on a chair that is initially at rest but can rotate. The tire is placed in a horizontal position and given a spin in the clockwise direction. The student then flips the tire so that the bottom of the tire is facing up. The chair rotates to the right - clockwise direction. Why? This is an illustration of conservation of momentum. Istudent+chair initialwstudent + chair initial + Itire initialwtire initial         = Istudent+chair finalwstudent + chair final + Itire final lwtire final   0 + Ltire = Istudent+chair finalwstudent + chair final  -L Where L for the tire was initially positive (positive taken as down direction) and because of the action of the student the direction was changed to up and therefore negative. But, since angular momentum is conserved (no outside net torque applied to the system), L is conserved. For this to happen, Istudent+chair finalwstudent + chair final must be = 2L The sign of angular velocity (w) must therefore be positive - in a clockwise direction.