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One can often see (hopefully only in the movies) that a bullet shot through a pane of window glass leaves a hole in it, but overall the glass is left largely intact. However, a low-speed projectile, e.g., a stone thrown into a window would probably shatter the glass completely. Is there a critical speed below which a bullet would shatter the whole window pane instead of piercing a hole?

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    $\begingroup$ I think only treated glass (e.g., multiply laminated panes) will have the hole after a bullet is fired while untreated glass will shatter as well. Do you have any examples of rocks & bullets being fired upon the same sheet of glass with the effect you describe? $\endgroup$
    – Kyle Kanos
    Commented Sep 18, 2014 at 2:21
  • $\begingroup$ Speed does matter: journals.aps.org/prl/abstract/10.1103/PhysRevLett.110.174302 $\endgroup$
    – Johannes
    Commented Sep 18, 2014 at 2:31
  • $\begingroup$ I think this PRL paper is very relevant, it says, "At low speeds (below 65 m/s for h=1mm), radial cracks extend until they reach the sides of the plate. At high impact speeds, the petals delimited by the radial cracks break to form circumferential cracks resembling the conical cracks characteristic of Hertzian fracture." $\endgroup$ Commented Sep 18, 2014 at 15:25

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The main factor you should consider is impulse: if the force acts for a longer interval of time, it causes greater fractures in your glass. If it acts for a shorter interval of time, it causes less fractures.

Again, it depends on the material of the glass and the projectile you are using.

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