# Friction as centripetal force...problem with the mass

1. May 29, 2015

### Geo louv

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

The problem is that if I have a 5kg mass and 1 kg mass at the same radius with the same μ....and I increase slowly the angular speed ω....then the first mass that will stop the circular motion is the one of the 5 kg mass because needs more centripetal force.Can someone say that this is not true and the two objects will stop at the same time the circular motion because ofthe equations T=m(u^2)/r μΝ=m(u^2)/r μ(mg)=m(u^2)/r. μg=(u^2)/r. ??????
2. Relevant equations

3. The attempt at a solution

2. May 29, 2015

### Geo louv

I have big problem......because if you see the equation μg=u^2/r you can assume that the two objects will leave at the same time.....

3. May 29, 2015

### deepakkumaar97

This is not true.

4. May 29, 2015

### Geo louv

Yes if you see the equation F=mω^2R......then you will come to the conclusion that the one with the bigger mass will stop first to moving circular because need more centripetal force..............Yes but also at the bigger mass I have bigger friction....T=μΝ. Τ=μ(mg)....so why two masses are not stopping the circular motion at the same time???????

5. May 29, 2015

### deepakkumaar97

They should stop at the same time.

6. May 29, 2015

### Geo louv

No...if you do the experiment the bigger mass stop first the circular motion

7. May 29, 2015

### SammyS

Staff Emeritus
This problem is not well defined. You haven't given enough details.

From the sparse description, I don't see how centripetal force is involved at all.

8. May 29, 2015

### Geo louv

9. May 29, 2015

### Geo louv

But m1 has also bigger friction......because of the bigger mass...so they must leave at the same time

10. May 29, 2015

### haruspex

Please describe the experiment in detail. Are they both resting on a flat rotating surface, perhaps? What are the shapes and widths of the objects, and how far are their mass centres from the axis?

11. May 30, 2015

### Geo louv

Haruspex you are GENIUS.....OF course if it is a float rotating surface...they will stop rotation at the same time....,but if it's not.....and the maximum Ts is the same then...the bigger mass will stop rotation first

12. May 30, 2015

### SammyS

Staff Emeritus
Please describe the experiment in detail.