# Units for Precession Rate (Ω)?

lightlightsup
Homework Statement:
The precession rate is given as ##Ω = \frac{Mgr}{Iω}##.
Relevant Equations:
What are the units here?: I'm calculating it as ##\frac{1}{rad . s}##.
The precession rate is given as ##Ω = \frac{Mgr}{Iω}##.
What are the units here?: I'm calculating it as ##\frac{1}{rad . s}##.
Am I supposed to interpret this as revolutions per second, sort of like frequency, and ignore the ##rad##?
Also, period is calculated as: ##T = \frac{2π}{Ω}##. So, ##T##'s units are ##\frac{s}{rev}##?
I'm guessing that I don't quite understand yet how ##rads## are ignored in the calculations.
Edit: This refers to gyroscopic precession wherein gravity is the only force causing a torque.

Last edited:

Mentor
Homework Statement: The precession rate is given as ##Ω = \frac{Mgr}{Iω}##.
Homework Equations: What are the units here?: I'm calculating it as ##\frac{1}{rad . s}##.
I get 1/s, which would be the same as the units for ω...

EDIT -- can you show the units you have for the first equation, and what you cancel to get your result?

lightlightsup
I get 1/s, which would be the same as the units for ω...

We're ignoring ##rads##, I guess? Because they are considered "dimensionless" ratios?

• berkeman
lightlightsup
I get 1/s, which would be the same as the units for ω...

EDIT -- can you show the units you have for the first equation, and what you cancel to get your result?

I'm sure there is some hole in my logic here somewhere.

Mentor
Since radians are dimensionless, don't carry them along as units. In that case, you get the correct units for Omega, IMO.