Final answer:
The combined weight of two blades contributes to the operational efficiency and stability of systems like wind turbines and helicopters, and the control in sports like figure skating by affecting moment of inertia and the pressure exerted.
Step-by-step explanation:
The combined weight of the two blades helps in several areas depending on the context. In the case of wind turbines, as described in the reference that the blades are akin to airplane wings, the weight is important for maintaining stability and ensuring efficient rotation to engage the wind at any angle.
In the case of helicopters, having blades with significant combined weight contributes to the moment of inertia. A higher moment of inertia means more energy is stored in the rotating system, which in turn helps maintain a steady rotation and provides stability against factors that might disrupt the rotation. The reference to helicopter blades rotating in opposite directions to negate the need for a tail rotor also leverages the combined weight of the blades to maintain stability and counteract the rotational effect on the helicopter's body.
Lastly, in the case of a figure skater as mentioned in the references, the combined weight distributed on two blades determines the pressure exerted on the ice, which allows for the fine control needed in skating movements.