Assume an incompressible, laminar fluid at a steady state passing through a non-uniform cross-sectional tube. As the fluid is incompressible, the volume of the fluid element and its mass remain constant. The speed of the fluid element entering and leaving the tube is different, resulting in net kinetic energy change. The force acting on the fluid element is due to the fluid's surrounding pressure. So, the net work done on the fluid element by the surrounding fluid during displacement is the difference between the work done while entering and leaving the tube. When the fluid element traverses in the elevated region, it gains gravitational potential energy and the change in gravitational potential energy is determined. According to the work-kinetic energy theorem, the net work done on the fluid element equals the change in kinetic energy. Dividing throughout by a common value, an equation is obtained. Along a streamline, the total energy per unit volume of a fluid flowing is a constant, termed the Bernoulli's equation.