# Angular momentum with gears

1. Aug 8, 2015

### george heck

Lets say one gear is rotating with some angular velocity and its angular momentum vector is pointing up.
A second gear (not rotating) is then allowed to mesh with the first. The second gear has the same radius and moment of inertia as the first.
Is not the angular momentum vector of the second gear pointing down since it rotates opposite to the first?
and if so, how is it that angular momentum is conserved as one gear will have positive and the other negative
angualar momentum - thus summing to zero, (after the "collision")?

thanks

2. Aug 8, 2015

### Qwertywerty

Hint : It isn't conserved . Look at the axle of the gears . Are they part of your system ?