What type of steam turbine moves the rotor by the force of reaction?

The reaction turbine is designed to harness the force of fluid reaction rather than relying solely on the impact of the fluid. In this type of turbine, steam enters the rotor blades at a higher pressure, and as it moves through the blades, it experiences a drop in pressure. This drop in pressure contributes to producing thrust against the blades, resulting in rotor movement.

The rotor of a reaction turbine is shaped in a way that allows the steam to expand and accelerate as it passes through the blades, which yields a continuous force throughout the blade passage. This contrasts with the impulse turbine, where the steam's kinetic energy is converted to mechanical energy through the impact on the blades without a significant change in pressure while passing through.

In summary, a reaction turbine primarily utilizes the principles of fluid dynamics to create motion through the reaction of steam being expanded within the blades, making it the correct choice for this question.