What is Bernoulli's principle concerned with?

Bernoulli's principle is fundamentally focused on the relationship between pressure and velocity within a fluid flow. This principle states that in a streamlined flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or potential energy. It can be observed in various applications, such as in airfoils where the air moving over the wing travels faster than the air beneath it, leading to a pressure difference that generates lift.

The other options refer to separate aspects of fluid dynamics and physics. The behavior of gases under varying temperatures pertains to the ideal gas law and thermodynamics, which describe how gas laws are affected by temperature changes. The effect of gravity on moving objects is a fundamental concept in mechanics, focusing on gravitational forces rather than fluid behavior. Lastly, the conservation of energy in mechanical systems relates to how energy is transferred and transformed in physical systems and is not limited to fluid dynamics. Each of these concepts highlights important principles, but they do not encapsulate Bernoulli's principle as specifically as the relationship between pressure and velocity in a fluid.