# Homework Help: Theoretical doubt with rolling without slipping

1. Jun 29, 2012

### Hernaner28

Hi. I'm taking a look at this problem:

And my doubt is with step 2 when he calculates the torque. He just says it is Fd. But...why? F only has a component which effectivly does torque.

Thanks

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2. Jun 29, 2012

### Infinitum

Hi Hernaner28!

F as a whole is the component which creates effective torque. Fn doesn't create torque as its line of action passes through the ball's center, and the same with mg. But F has a line of action that is at a distance 'd' away from the center and perpendicular to it. So...

3. Jun 29, 2012

### Hernaner28

I don't understand. F has a tangential component and that's the one which creates torque, the other component of F doesn't create torque because it passes through the center. Maybe it's a geometric problem I cannot solve...

Thanks!

4. Jun 29, 2012

### Infinitum

Yes. But both the torques, that is the torque taken with the tangential component, or just taken the way it is, give you the same result!! That's because for the tangential component, the perpendicular distance from the center is R, but in the case of the force given, it is d. Think about it...

5. Jun 29, 2012

### Hernaner28

Ahhmmm I see... I didn't know you could take that easy way.. Thanks!