Why can you see through water? (From a real 4 y.o.)
In: Physics
All things in the world are made up of tiny building blocks called atoms, and molecules (which are like blocks of atoms arranged in particular shapes, like how you have lego bricks that are 2×4 or 3×1 or a 2×1 slant, and so on).
Whether you can see through something depends in what molecules the thing is made from, what shapes and how far apart they are.
Different colours of light have different sizes (different wavelengths), and if the object the light hits has exactly the right molecules and shapes, the bits of light that hit it can fit exactly into the spaces around the molecules and they get absorbed/trapped by the molecules in the object, and so the bits of light don’t pass through it.
But if the spaces around the molecules is not exactly the right shape for the colour of light, the light can bounce through the object and come out the other side where it can go into your eye and you can see it.
For something like water, the reason you can see through it is because the molecules are the wrong shape to absorb light in what we call the “visible spectrum”, which is all the colours of the rainbow from red to indigo/violet. Any light of any of those colours will bounce through the water and come out the other side where you can see it.
But with water in particular, the molecules are the right shape to absorb a different type of light – water is very good at absorbing microwave light, which is a type of light that you can’t see with your eye. That’s why food gets hot in the microwave oven – it spits out a bunch of microwave light, and all the water in the food traps those bits of microwave light, which makes the water heat up and makes your food hot.
You can see thanks to light (from the Sun or a lamp or whatever).
Water, like air and glass, is transparent. This means that when light reaches water, most light passes through the water without being “absorbed” (blocked) or “scattered” (bounced back).
Therefore you can see through water, or air, or glass.
Objects are transparent or not depending on how they are made inside, in particular how extremely tiny particles are made and positioned.
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.
Because the energy of visible light doesn’t match the energy levels of the electrons around the molecules. Since you can’t split the energy of a photon in two, there needs to be a match in energy for any interaction/absorption to take place. It’s like trying to purchase something for $50, but you only have a $100 note and the cashier doesn’t have any change (and assuming you’re not allowed to overpay :).
Since no interaction can take place, the light just moves along and the object is perceived as transparent.
So a lot of the other answers here are talking about HOW we can see through water, but I’m gonna talk about WHY.
We evolved from things that lived in the water, a lot like fish. Think about it like being your great great great great times a billion grandfather was a lil fishy thing. These things lived in the water, and being able to see things was a HUGE help when they were living there. So they evolved to be able to see in water, and we still are able to today
Latest Answers