Final answer:
A trailer bouncing up and down slowly on a highway is likely nearly empty, as there is less mass to dampen the oscillations of the suspension springs.
Step-by-step explanation:
When observing a trailer on a highway, the dynamics of the trailer can hint towards its load weight. A heavily loaded trailer will have less bounce because the mass of the load dampens the spring's oscillations in the suspension system, causing the trailer to move more smoothly. In contrast, an empty trailer is more prone to bounces and oscillations, as there is less mass to dampen the movement of the springs. Thus, if a trailer is bouncing up and down slowly, it is more likely to be nearly empty, since the springs are less restricted and can oscillate more freely without the weight of a heavy load.