- #1

- 3,962

- 20

I have two simple scenarios.

__First scenario.__

We have two identical flywheel devices. When spun up to speed they retain their angular momentum for a long time due to very efficient bearings. Once per revolution they emit a light signal giving an indication of their rotation speed. They are both spun up to X rpm and their flashing beacons flash at Y Hertz. One is slowly lowered down a shaft into a gravitational well, to a depth such that the gravitational red shift factor is 4.

Q1) What is the rpm of the flywheel as measured by a local observer at the bottom of the shaft?

Q2) What is the flashing rate in Hertz of the flywheel at the bottom according to an observer at the top?

__Second scenario.__

This time one flywheel is stationary at the bottom and the other is stationary at the top. Both flywheels initially have zero angular momentum. The flywheel at the top is spun up to X rpm. The flywheels have a radius of 1 metre and mass of 4 kg, so the moment of inertia of the flywheels is 2. Assume the energy required to spin up the top flywheel to X rpm is Z joules. The flywheel is connected to a generator and then to a light source that is transmitted downwards. The light energy is collected by a transducer and the bottom and powers a motor to spin up the lower flywheel. Assuming negligible power losses:

3) What will the rpm of the lower flywheel be according to local observer when all the energy from the top flywheel is transferred to the lower flywheel?

4) What is the flashing rate in Hertz of the flywheel at the bottom according to an observer at the top, when all the energy is transferred?

**This is not a homework or textbook question.**It is a direct extension of the previous thread here: https://www.physicsforums.com/showthread.php?p=3387677#post3387677