# Rotating masses

1. Jul 9, 2011

### luk4rite

How does the angular velocity change with increase in the mass?
For example : if there is a shaft rotating at 1500 Rpm , then if a disc of 5 kg is fastened , does the angular velocity of the disc will be same as 1500 RPM , and what happens to the RPM if the disc mass is 50Kg.

2. Jul 9, 2011

### Fewmet

Momentum (angular or translational) is conserved. If the extra mass were simply attached from rest to the shaft, the mass would go from I$\omega$=0 to some rotational momentum greater that zero. The spinning shaft would have to lose enough angular velocity such that the sum of the rotational momenta (those of the 5 Kg mass and of the shaft) was the same.