Why can air be compressed but liquids can’t?
In: Physics
This is precisely why you need a turbo charger to get more power out of your engine. (Four stroke internal combustion gasoline powered engine, that is.)
You can always squirt in more gasoline using the fuel injectors, no problem. Because the liquid basically does not compress.
But technically the “fuel“ needed by your engine is the mixture of both gasoline and air. And you cannot just squirt in more air. The only way to get more air in, when you squirt in more gasoline, is to first compress that air so there is enough of it to be matched with the additional gasoline.
This is how you increase the total “fuel“ injected into the cylinder prior to combustion. And this is why a turbo charged engine is more powerful, because it can use more fuel, by compressing the air.
Oh and by the way it’s called a “turbo“ charger because it has a turbine. (And the turbine spins by using the exhaust coming from the engine.) And that turbine is connected to a compressor, which is what compresses the air.
So this is a real-world, practical answer to your question: gasoline does not compress, air does, and you can see that in action in a turbo charged engine.
You can compress them a little bit, but it’s generally much harder than with a gas.
One of the things that makes a liquid a liquid, and not a gas, is that the molecules in a liquid interact with each other strongly. In a gas, molecules mostly don’t interact unless a couple happen to collide and bounce off each other. But in a liquid each molecule is connected to its neighbors by intermolecular interactions. This is especially notable with water molecules hydrogen bonding to each other, but other things do it to.
These interactions are why if you put liquid into a container, it hangs out at the bottom instead of expanding to fill the whole container like a gas would. The molecules are basically stuck together
In order to have these interactions in the first place and be classed as a liquid, molecules have to already be pretty close to each other so you can’t easily squeeze them closer together. And the molecular forces try to keep them a certain distance apart, causing them to resist squeezing further. In contrast, there’s a lot of extra space with gasses and you can squeeze them until the molecules are much closer together (at which point they often start interacting and become a liquid).
So liquids are not very compressible, while gasses are very compressible.
What do you think water pressure is? Liquids can totally be compressed. Liquids and gases are even lumped into the same branch of science: [fluid mechanics](https://en.wikipedia.org/wiki/Fluid_mechanics)
Gasses are more obviously compressed than liquids. Even metal can be compressed. In fact, compression of metal is what makes some nuclear weapons do their thing… it shoves the mass of metal to a higher density. But only for a tiny amount of time. But the results of doing so is quite spectacular. Or so I’m told.
Water can expand up to 1700 times when evaporating. There will be significantly more empty space between the molecules that can be removed when it’s in gas form than when it is in liquid form.
Liquids and solids can be compressed. The fact sound waves can travel through it shows some level of compression.
With enough force, the amount of compression can be quite large. The plutonium core of an atomic bomb is compressed by a fact of 2 to 3 by the conventional explosives that drive the implosion.
Imagine you and two friends are on a play ground. You can jump around and run. You are like a gas. But if needet all of you can squeez in in little play house. Now you are compressed.
Now Imagine you are Holding Handys with your friends. You can still move a bit but not as much as before. Now you are a liquid.
Maybe it is possible to Compress you a little bit, but not as much as before, when you where a gas.
If you Co press a Gas enough it will become liquid and mayve even Solid.
It’s about the same as crumpling a piece of paper. The more compact you go, the harder it gets. To the point where it may seem that you can’t compact it anymore. It’s compact enough for you to stand on it, even though it’s still possible to get it more compact, to your perception it can’t be compacted anymore.
So both gasses and liquids can be compressed, they just require a different amount of force.
Liquid can and does compress, but water is particularly bad at it because it’s a highly polar molecule.
Gasses are more compressible, in general, because the moleculed within them have greater degrees of freedom.
Imagine trying to tell a group of people to squish together.
Gas is like having a room with 10 people in it and telling them to get closer.
Liquids are like having the same size room with 100 people in it and telling them to get closer.
Water is like having the same size room with 100 people, but none of them use deodorant and they all hate each other.
And since we’re on the subject, solids are like the same size room with anywhere from 100-1,000 people but they all have to stand in a certain place and if you make them squish the room breaks and the people fly off in different directions.
It can be, hence hydraulics, but not nearly as much as gases. There’s more space between the molecules in gases than there is in liquids.
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