[ELI5] If water is incompressible, how do we have things like power washers and (nuclear) PRWs?
In: Engineering
It’s not incompressible. It’s just very hard to compress compared to gasses like air.
Everything can be compressed, even solids
I think you’re mixing up a couple concepts.
First as the other comment says, most of the time incompressible just means very hard to compress.
Second, power washers and nuclear prw uses PRESSURIZED water, which is essentially much force is applied on the water. The pressure has the side effect of compression but not very much. For reference, Google says PWR reactors sit around 15 Megapascals, at that pressure, 1L of water gets compressed 0.00725L. Basically not at all.
Nothing is incompressible, and water is no exception. It’s only incompressible in comparison to really compressible stuff like air. It’s much harder to squish a cube of steel than it is to squish a cube of water, but you can squish both.
But the ability to use water to exert pressure / the ability to pressurize water doesn’t rely on water being compressible at all.
Imagine a world where water is truly incompressible. What that means is that if you push on water, you can’t reduce its volume. But that doesn’t mean the force you’re using to push on the water just disappears. Remember Newton’s Third Law. If you start pressing on something, it presses back on you. So if you push down with a force of 100 newtons on a lid with an area of one square meter of a tub containing water, that water gets an extra 100 pascals of pressure.
Imagine you have a hole in the bottom of that tub, and you start pressing on the lid. Shouldn’t the water come out faster when you press on the lid? Of course it should. Why does it? The force you exert on the lid is traveling into the water to make it go out faster than it would if you weren’t pressing on it. This doesn’t mean you’re compressing the water. You’re pushing on molecules of water, that are pushing on other molecules, that are pushing on other molecules, and so on until you get to the ones near the hole, which don’t have a wall to push on so they end up squirting out the hole.
Imagine a long tube full of billiard balls
They are, to a rough approximation, incompressible
If you gently push a new ball into the end, one will plop out the other end
If you push one really hard into one end, one will going flying out the other end
Pressure washers are just pushing really hard on lots of little tiny balls
It doesn’t explode while it’s running without the trigger pulled because there’s a valve that lets water back out to the inlet of the pump
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