1. Nov 5, 2011

### EinsteinKillr

1. The problem statement, all variables and given/known data

I'm working a problem concerning centrifugal acceleration and I've stumbled on something I don't quite understand:

2. Relevant equations

So the resulting units: kg * m*rad2/s2

3. The attempt at a solution

I would expect acceleration to be in unit ms-2

What's up with these radians? What do they mean?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Nov 5, 2011

### grzz

Note that there is 'linear acceleration' (i.e. rate of change of linear volocity) in m/s^2
and 'angular acceleration' (i.e. rate of change of angular velocity) in mrad/s^2 but of course radian is not an S.I. unit.

Last edited: Nov 5, 2011
3. Nov 5, 2011

### Staff: Mentor

The radian is a dimensionless quantity. It's a unit of angle (really a ratio) that has no dimension, so the final units of acceleration will be m/s2 as expected. (See: http://en.wikipedia.org/wiki/Radian#Dimensional_analysis)

4. Nov 5, 2011

### grzz

'radian' is a measure for an angle.
For example pi radians is equivalent to 180 degrees.

5. Nov 5, 2011

### EinsteinKillr

I've never consider that a radian is a ratio of a circle. Thanks! that makes a lot more sense.