Comments by "Scott Franco" (@scottfranco1962) on "Can a Solid Glass Ball Stop a 50cal???" video.

  1. This is classic compressive spalling. To such a compressive shock, a glass ball can be very hard. Recall that glass is actually a liquid, abet a very slowly moving one (there are examples of Roman glass vases that have slowly collapsed under a load). Thus for microseconds, the ball is, essentially, bulletproof. However, the impact sets up powerful shockwaves in the glass. It compresses, and then rebounds. That rebound contains enough force to break the glass off the surface in sheets (spalling), because the glass is more able to resist the force compressing it than the counterwave expanding outwards. The waves can go anywhere in the glass, including to the opposite side. The shape of the glass probably focused the waves to the opposite side. I have observed a similar effect when hitting bottles with a lead pellet gun. The pellet is deformed in the shape of the bottle, and this matches what I saw, abet in very rapid succession. The lead pellet hits the bottle, is completely stopped, and drops off the bottle. However, the shock waves criscross the bottle, and it shatters from the force of the shockwaves. I observed that because I saw a short period of time between the time the pellet hit the bottle, and the time the bottle shattered.
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