Inertia [NLM for IIT JEE]

 Query :

When a bullet passes through a window glass, it makes a hole, but a stone passes making crack and smashing the window. Why?

[Example of Inertia of Rest]

Answer :

💠 When a bullet is fired and hits the glass, the part of glass which comes in contact with the bullet immediately has a tendency to share the large velocity of bullet.

💠Due to large velocity, it has less time of contact, thus less change in momentum. This less impulse is offered to the other parts due to inertia of rest.

Glass hit by bullet making a tiny hole.
[Larger velocity, less time of impact or contact, less area to which force experienced , thus hole formed]

💠Only a hole part has the most impulse and thus it gains the velocity of bullet & thus the hole is formed.

💠When a stone with low velocity strikes the glass, the surrounding part of glass has enough time to share a greater impulse (due to more time) , Force imparted has much time for spreading throughout the glass & thus the glass is impacted at more surface area causing crack on the glass.

Credit: Shutterstock

Main reason is that due to inertia of rest of glass pane means glass pane is not eager to simply move along the force imparted.