Velocity is the rate of change of displacement of fluid particles with respect to time. It represents how fast the fluid is moving. The formula for velocity ($v$) in fluid mechanics is simply:

Where:

• $v$ is the velocity (in meters per second, m/s).
• d/dt​ denotes the derivative with respect to time.
• $d$ represents the displacement or distance traveled by the fluid particles.
• $dt$ represents the change in time.