Final answer:
A trailer bouncing slowly on a highway is likely nearly empty because less mass means more susceptibility to bounce with road irregularities, as opposed to a heavily loaded trailer which would bounce less due to more weight absorbing road impacts.
Step-by-step explanation:
When you observe a trailer on the highway bouncing up and down slowly, it is more likely that the trailer is nearly empty.
This behavior is due to the fact that an empty trailer has less mass, making it more susceptible to vertical movements from irregularities on the road surface.
In contrast, a heavily loaded trailer would have more mass, which would generally lead to less bouncing, as the additional weight would help absorb the impact of bumps and irregularities, leading to smoother motion.
This is because a heavily loaded trailer will have more inertia, which causes it to bounce less compared to an empty trailer. The inertia of the loaded trailer helps to dampen the bouncing motion.