Why can you see through water? (From a real 4 y.o.)
In: Physics
You can see through it because it’s not opaque, and the reasons for opaqueness have to do with absorption and scattering, both of which water happens to lack.
When light hits an object, what is happening on the very small scale is that photons are interacting with the electron clouds of atoms and molecules. Depending on the situation of the atoms involved, the photon might be absorbed and then re-emitted. This might change the properties of the photon, and thereby, makes that material look opaque to us: photons aren’t passing through the object unhindered so we can’t see what’s behind the object. On the other hand the atoms might happen to be in such a state that the photons emitted have the exact same momentum, energy, and direction as when they were absorbed. This will look transparent to us, because photons carrying the same information from objects behind this object will make it to our eyes.
Also, water is a liquid, so it can’t be have air gaps or cracks in it that would cause scattering. Scattering happens when the photons bounce around in every which way due to the material properties of the whatever you’re looking at. This is why snow – which, because of it’s crystal structure, has a lot of air gaps – is opaque, but liquid water is transparent.
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