Final answer:
Seats should have springs that enable them to return to a lifted position, based on the principles of physics related to mass-spring systems and the conversion of kinetic to potential energy during oscillation.
Step-by-step explanation:
The statement 'Seats should be sprung to return to a lifted position' implies the application of physics principles, particularly related to potential and kinetic energy in a mass-spring system.
In such a system, like the one depicted in Figure 8.4, when the mass is released from the unstretched position (point A), it moves past the equilibrium point (point B) due to its kinetic energy. When the spring reaches its maximum extension at point C, the kinetic energy is converted to potential energy, and the force of the spring will cause the seat, in this case, to return to a lifted position. This process is akin to oscillation, where the mass-spring system exhibits periodic motion.