I straggle with getting full grasp of concept for Cavitation. I was finding statement that : If The pressure of fluid is lower or equal to the Vapor Pressure then it will start to boiling. And I can't understood the reason behind this. Why actually it happens? I understood where we came to the vapor pressure concept in closed system ( containter with lid). And this balance. And let say we have a vapor pressure equal 80kPa. Nothing is going to do in 20 o C. Then we reduce the pressure in container and it start to boiling. But why? It's hard to understand for me what is the reason for that? Because the pressure of liquid is higher then vapor? And if we go further when we have opened lid it's even harded to imagine this. We have atmospheric pressure equal ~100 kPa. Then what is the value of vapor pressure? Is it equal then to atmospheric? If it's the partial pressure then it's a sum of some other pressure with atmospheric one? I don't know how to clear those things. More to say that cavitation is if the liquid pressure is lower the vapor pressure or equal. Additionally is the vapor pressure exist in the ocean? (under water)? If the cavitation occure on the pressure lower the vapor how it's possible? I was think about this cavitation as a pressure necesseary to be higher then pressure vapor to overcome it. But it's looks like it don't work like forces balance in mechanics. Is it like from higher pressure to lower and then this block the boiling?