eli5 – How can the human body be composed of 70% water when it feels and behaves like any other solid?
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Is a grape a solid? Is it *more* or *less* solid than a raisin?
A raisin is 15% or less water, and a grape is about 75% water. The difference in size is purely based on the removed water.
People, like grapes, can have physical structures that store a lot of water while having a relatively solid outer surface.
States of matter are determined by the energy of the matter and how its bond conform inside the material. The human body holds a rigid shape and doesn’t just puddle into whatever container it’s in. How soft pliable or squishy something is doesn’t matter, only how it does or doesn’t hold itself together
Does it though? How many other solids are squishy and have maliable joints?
Your bones are mostly hollow matrices of mineralized bone tissue. But even bones contain mostly water-mediated tissues.
While water might constitute 70 percent of your mass, the water is divided between and contained within billions of cells, each within its own phospholipid membrane that surrounds cellular plasma (again, mostly water) organelles made from proteins, and a nucleus that contains your DNA.
That our bodies appear solid is simply a heuristic presumption our brains makes because such is the most practically useful way to conceptualize the human body.
Take the amount of water that’s inside a human body and just pour it all into a big bag. It sloshes around a lot and feels like a liquid, right? Your question is asking why people *don’t* feel like that.
Well, take all of that water, and split it up among several billion teeny tiny boxes. Put all those boxes together in the shape of a human, and it’ll contain the exact same amount of water as the big bag did, except now it’ll feel solid because the water is all held within objects which have shape and structure.
In an actual human, those billions of teeny tiny boxes are all of the cells in the body.
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Because the water is locked up in zillions of cells, which are surrounded by cellular membranes, giving them a stiffness. A Tomato is 95% water. But it feels solid when you pick it up. Same reason
Think of it this way: Take a basketball. Cut a hole in it. Fill it with water. The basketball is now something like 90% water. But when you touch it, it feels solid. Shrink that basketball down to celluar size, and put a zillion of them together to make a human, and you have a solid feeling human that is mostly water.
Suppose you have a huge metal water tank filled with water. You can probably get pretty close to 100% water by volume. But the tank is solid, and will feel very much like a solid if you hit it.
From the outside you can’t immediately tell that the tank is mostly water.
There a lot of good answers here but I’ll add this note: humans *aren’t* 70% water. We’re closer to 50% (females tend to be lower, males tend to be higher), but even that percentage will fluctuate quite a bit during the day.
A bottle of beer is like 95% water but if I hit you around the head with it you would probably not accept the excuse that I was just washing your hair.
Think about a Car Tire. It’s composed of 70% air by volume but certainly doesn’t feel like air does it? That is how much of a effect the other 30% can have.
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