What does Bernoulli's equation assume about fluid flow?

Bernoulli's equation assumes that the fluid flow is incompressible, which means that the fluid density remains constant throughout the flow. This assumption is critical because Bernoulli's equation derives from the principle of conservation of energy for fluid elements moving along a streamline. If a fluid were compressible, such as gases at high velocities or under significant pressure variations, the density would change, complicating the application of Bernoulli's equation.

In incompressible flow, we can treat the fluid as having a uniform density, which allows the relationship between pressure, velocity, and elevation to be straightforwardly expressed in the equation. This simplicity is essential for accurately predicting how pressure changes in relation to fluid speed and height in various engineering and physics applications.