# Inertia of a bowling pin

1. Oct 1, 2004

### ddoucet

Hi,

I need to know the moment of inertia of a bowling pin. I'd like to know how to calculate it. I would prefer an approximation formula according to the mass of the pin instead of an integration method.

Thank you

2. Oct 1, 2004

### HallsofIvy

Staff Emeritus
The moment of inertia about what axis?

3. Oct 1, 2004

4. Oct 1, 2004

### Sirus

Where does the axis intersect with the pin? Any formula you develop here will be an approximation since the bowling pin has such an irregular shape that cannot be dimensionally defined (like, for example, a sphere can). If you know the length of the pin, you can assume it is a uniform horizontal bar, at which point you can use the formula for that, or derive it using calculus.

5. Oct 4, 2004

### ddoucet

The pin height = 38.1 cm
The pin mass center height : 14.68m

I think that it's possible to have a very good approximation of the bowling pin volume by using few spheres. In my application, the pins are represented by 6 spheres.

6. Oct 7, 2004

### ddoucet

Any idea about an integration method that I could use ?

7. Oct 8, 2004

### Sirus

Wouldn't using the formula for a uniform bar be a better approximation? I forget exactly what the formula is, but you can find that online or in a book somewhere.

8. Oct 14, 2004

### ddoucet

I'm now using the moment of inertia of a cylinder on it's transversal axis :

I = 1/12 * mh^2 + 1/4 * mr^2

But since the mass of a pin is less uniformly dispersed than the one of a cylinder, I would have think that it's inertia would be lower.

9. Oct 14, 2004

### reilly

Why not try three linked cylinders, or more.That is, build a bowling pin with cylinders -- that, in fact, is one way of simulating the z integral -- if z is the axis of symmetry. And, don't forget the other moments.
Regards,
Reilly Atkinson

10. Dec 22, 2005

### rajni0003

Hi,
Can anyone explain whole physics of falling of ppin due to bowl - i mean forces on pins ,its rotations etc..