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1:15 AM
Q: Why do bullets shoot through water but not through sand?

Árpád SzendreiThere are a few questions only on this site about this but none of them answer my question. Can cannonballs go through water? Why does a bullet bounce off water? I find it hard to understand why bullets shoot through water at longer distances but stop in sand almost right away: Both water and sa...

3 hours later…
4:32 AM
Q: Speed of sound and Water ripples speed are the same?

Pedro PinhoWhen a droplet of water hits the surface of a lake it produces ripples that travel outward. My conception is that it travels at the speed of sound on water (since sound are nothing less that perturbations on the medium). But ripples travel much slower than that. What's happening? Is my conception...

6 hours later…
10:17 AM
Q: How to explain apparent acceleration due to the expansion of the universe and inertial reference frames

EoinIn Newtonian physics, object A observes the acceleration of object B precisely when A observes a net force acting on B. How should we understand perceived acceleration under the observed expansion of the universe? Can it be attributed to a force? Does this mean that there is no such thing as an "...


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