Hi!

Can someone please explain to me: What does Bernoulli's principle really mean? I don't get the formula.

First of all, velocity has a direction. And second velocity is relative. Let me explain what I mean: Bernoulli's principle says that

if we derive this by some variable x, we get:

This would mean that if the velocity is high from the beginning, the value of

is of big importance to the equation, but if the velocity is zero, the value of

doesn't matter at all? Can a liquid be "still"? In that case, in relation to what is the velocity of the liquid measured?