Not a pebble( though I mean. It's possible), it's normally a piece of broken ceramic. It works because the ceramic breaks down to a molecular level, so when it hits the energy is all focused down to that level, breaking the glass due to its inability to spread out the impact(applied force, work, etc).
Often times people break spark plugs to get the ceramic, as they have a special, harder variety.
2020-04-06 14:26:46 +0000 UTC
Isnβt there some kind of pebble that breaks glass windshields? Obviously this is not that, but it got me thinking....how does that even work?