# Help needed to convert angular velocity to angular acceleration

1. Jun 25, 2013

### sherazi21st

hi,

I've calculated
ω=5 rad/s

How can I calculate angular acceleration (α)
I've Mass, M=4Kg
Radius, R = 2m
and time taken by each single revolution, T=3sec.

2. Jun 25, 2013

### Staff: Mentor

Unless you forgot to tell us something, the angular acceleration is zero!

3. Jun 25, 2013

### sherazi21st

I've only this data, what is missing?

4. Jun 25, 2013

### Staff: Mentor

How the angular velocity is changing.

Are you sure you want angular acceleration, not centripetal acceleration?

5. Jun 25, 2013

### sherazi21st

I had also the same point but I got this data only. I thought there may be any method to convert this by either convert this ang. vel. to tang. vel. by rw and then it might be converted in to angular acc. by using definition of centripetal acc. or something else if I'm not wrong.

6. Jun 25, 2013

### Staff: Mentor

Angular acceleration is related to tangential acceleration, not centripetal acceleration. But all you gave us is an angular velocity.

You need to describe what you are being asked to find in more detail. What did you measure? What physics topic are you studying now?

7. Jun 25, 2013

### sherazi21st

Can you tell me how will we calculate Centripetal acceleration? Just by converting w in to v and then putting v in v^2/r. Am I correct?

8. Jun 25, 2013

### sherazi21st

Dear, I'm studying Angular acceleration and angular velocity. I am given only radius of the horizontal circle in which a mass m is moving and completes one revolution in t seconds. I guess there is fault in the question.

9. Jun 25, 2013

### Staff: Mentor

Sure. You can also use this equivalent expression and save yourself the conversion: ac = ω2r

10. Jun 25, 2013

### Staff: Mentor

Is it moving with constant speed, or does it start from rest (for instance)?

11. Jun 25, 2013

### sherazi21st

constant w

12. Jun 25, 2013

### Staff: Mentor

In that case, the angular acceleration is zero, as pointed out by russ_watters earlier.

13. Jun 25, 2013

### nasu

It's either T =3s OR w=5 rad/s.
You cannot have both for the same motion, with constant angular speed.

If T=3s, the angular velocity is about 2 rad/s.

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