Final answer:
The point about which a helicopter would balance if suspended is known as the center of gravity. This point is vital for helicopter stability and control during flight and is distinct from other related concepts like lift coefficient, rotational axis, and thrust vector.
Step-by-step explanation:
The point about which the helicopter would balance if suspended is called the center of gravity. This is because the center of gravity is the point at which the entire weight of the helicopter is equally distributed in all directions, and it is the point around which the object can rotate while maintaining equilibrium. This aspect of physics is essential for helicopters, as it affects their stability and control during flight. The other options provided in the list – Lift coefficient, Rotational axis, Thrust vector – are also related to the physics of flying objects but do not define the balancing point of an object.
For example, the lift coefficient is associated with the amount of lift a wing generates at a given airspeed, the rotational axis is the line around which an object rotates, and the thrust vector indicates the direction of the propulsive force. In the case of helicopters, the tail rotor helps in preventing rotation of the helicopter body due to its interaction with the main rotor's angular momentum. Thus, understanding the center of gravity is crucial for designing and controlling helicopters, especially considering the dynamic stresses and forces involved in flight.