Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: Why does one impart 'spin' to a bullet?

Learn more physics!

Most recent answer: 01/05/2015
Q:
A rifle Barrel has a spiral groove which imparts spin to the bullet. Why?
- Ajay Gautam (age 18)
Sonipat , Haryana , India
A:

Hello Ajay,

Because it improves the stability of the bullet's trajectory.  

All objects have three principal axes of rotation with corresponding moments of inertia.   Call them I1 ,  I2and  I3 with I1  <  I2  <  I3 .   It turns out that if an object is spinning about I1  or  I3  then its angular motion is stable against small perturbations.  On the other hand if it is spinning about I2 then it will 'tumble' chaotically.   For a bullet, tumbling is not a good thing since the varying wind resistance will tend to move it off course.   For the special case where I1  =  I2  the object will be stable when spun along the common  axis.

This phenomenon is described in 

 

LeeH


(published on 01/05/2015)

Follow-up on this answer.