A bullet makes a hole but a rock shatters the glass Consider a bullet fired toward a pane of glass. Barring slight cracks, it creates a relatively clean hole in the glass. On the other hand, when a stone is projected toward the same glass pane, it is observed that the glass pane immediately shatters. 
I have searched and searched for a convincing answer and the same question even exists on the website "Physics Forum". However, none of the answers are satisfying. Some say that this is due to the greater inertia of the glass against the bullet compared to the smaller inertia of the same against the. Others seem to agree that it is due to the higher momentum(and shorter time) of the bullet. 
What is the correct explanation for this? 
 A: As soon as one object impacts another, a pressure wave starts to propagate - this wave "tells the object" that it has been hit.
Now the peak value of the stress is a function of the rate at which the glass is being compressed, and of the rate with which the glass moves. If a region a short distance away "doesn't yet know" about the displacement of the glass at the point of impact, then there is a strong local shear / curvature in the glass. When this strain exceeds the limits of the material (glass) it will fracture. Since the bullet is traveling very fast, the wave has not traveled very far in the glass, and all the displacement is in a very small region.
By contrast, a large rock hitting the glass slowly will cause deflection of the entire surface before the local stress becomes very large. This results in the storage of elastic energy over the entire plate - and once a crack initiates (at the point of highest effective stress: actual stress possibly amplified by a stress concentration factor like a small surface crack or other discontinuity) it will propagate throughout the stretched medium (as the crack tip becomes a stress concentrator, it will propagate into regions of lower stress).
Crack propagation stops when the crack reaches a region with insufficient elastic energy stored. In the case of the bullet, the region where stress had time to build up is small.
In summary, the factors to consider are:


*

*The time to reach sufficiently night impact stress

*The propagation velocity of the stress wave in the glass

*The crack propagation velocity

A: This is because the impulse of the bullet is less than that of the stone. $J=F\,dt$. But, in the case of a bullet, dt is very small due to its high speed. Thus, it is able to impart its momentum to only a small area thus creating a neat hole. But the stone has a velocity much less than the bullet. Thus, dt is greater. It gets more time to impart its momentum and that too over a larger  area. This shatters the glass.
