In a reaction turbine, what primarily contributes to thrust generation?

In a reaction turbine, thrust generation is primarily a result of the pressure drop through the blades. This occurs because as steam passes through the turbine, it expands and loses pressure. The blades are designed to harness this pressure drop effectively, converting the potential energy of the steam into kinetic energy, which leads to rotational motion.

As steam enters the turbine, it causes a high-pressure area to exist on one side of the blades and a lower pressure on the other. This pressure difference creates a force that contributes to thrust, driving the turbine's rotor. The design of reaction turbines allows them to utilize both the kinetic energy from the velocity of the steam and the pressure differential across the blades for efficient energy conversion.

The other options do relate to various aspects of turbine operation but do not directly account for thrust in the same fundamental way. High-speed exhaust gases pertain more to the energy extraction process rather than thrust. The amount of steam used can influence power output but is not the primary factor in thrust generation itself. Similarly, pressure from bearings is important for supporting the turbine's components but does not contribute to the generation of thrust in the context of steam flow through the blades.