The correct answer is: A. velocity.
The velocity of a fluid is the rate of change of its position with respect to time. It is a vector quantity, meaning that it has both magnitude and direction. The magnitude of the velocity is the speed of the fluid, and the direction of the velocity is the direction in which the fluid is moving.
The velocity of a fluid can be measured in a number of ways. One common method is to use a velocity meter, which is a device that uses a probe to measure the speed of the fluid at a particular point. Another method is to use a Pitot tube, which is a device that measures the pressure difference between two points in the fluid. The pressure difference can then be used to calculate the velocity of the fluid.
The velocity of a fluid is important in a number of applications. For example, it is used to calculate the power of a fluid turbine, the rate of flow of a fluid through a pipe, and the drag force on an object moving through a fluid.
The other options are incorrect because:
- Discharge is the volume of fluid that flows through a given area in a given amount of time.
- Head is the energy per unit weight of a fluid that is due to the height of the fluid.
- Pressure is the force per unit area exerted by a fluid.