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I can't find this anywhere. If a drop of water hits a glass for example, at the speed of a bullet, will it damage it? Or will it just make the same as a raindrop?

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    $\begingroup$ One drop probably will have no effect. However, there are devices that use this principle to cut materials without making sparks. Such devices use a continuous stream of very high speed water, and they are very effective. $\endgroup$ Commented Aug 21, 2018 at 15:29
  • $\begingroup$ Well, hailstones regularly break glass and they are going nowhere near as fast as a bullet. $\endgroup$
    – zeta-band
    Commented Aug 21, 2018 at 15:50
  • $\begingroup$ Thanks to all of you who have answered this. For the curious, I've asked this because I'm writing a novel where a character shots drops of water, and I was thinking if it shoud be ice instead, because it's stronger. But I think the consensus here is that, at enough speed, i can cause damages. $\endgroup$
    – Vicioxis
    Commented Aug 21, 2018 at 16:21
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    $\begingroup$ A water drop (of the usual kind) wouldn't even be able to move at that speed -- it would immediately fall apart into smaller droplets. If at all, this would have to be a tiny water droplet, and it would slow down extremely quickly! So if you want to shoot at any non-tiny distance, it would most likely be impossible. $\endgroup$ Commented Aug 21, 2018 at 16:34

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Wet steam erosion is a big problem in steam turbine design, as you can see from this image:

enter image description here

So yes, water droplets with enough energy can certainly cause damage to even objects made of steel. With enough energy, it could certainly cause damage (or destroy) your glass.

Water jet cutting is another good example of high-energy water being used to damage (cut) something:

enter image description here

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It depends on a lot of things.

How big is the drop, and how fast is it moving, really? Most raindrops are smaller and less dense than most bullets, so in general a water drop moving at the same velocity as a bullet will carry less kinetic energy. Since a water droplet isn't a hard object, that energy also will be distributed over a longer interval than a bullet impact. So, it would likely be less damaging than the bullet.

Will it "damage" your glass? That depends on the glass. After all, some glass resists bullets.

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I think the drop of water is too light to cause a damage to your front window of a car. Since, the drop is not rigid, distortion occurs in itself causes a vary quick reformation in the spatial arrangements of the molecules and can break subsequent hydrogen bonding of water, which is more unlikely in the causualty of damages. Moreover water can beswept out easily due to the less adhesive property and small coefficient of restitution. Thus apart from the formation of ice crystals, it can't damage a hard glass, but may break a weak one, depending upon the nature of the glass concerned.

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  • $\begingroup$ I don't understand how a high speed droplet would form ice crystals? That seems like it cam from nowhere. $\endgroup$
    – JMac
    Commented Aug 21, 2018 at 17:23

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