Final answer:
Trailer bouncing up and down on a highway likely indicates a heavily loaded trailer rather than one that is nearly empty.
Step-by-step explanation:
When a trailer bounces up and down slowly as you pass a freight truck on the highway, it is more likely that the trailer is heavily loaded. This bouncing motion, known as vertical oscillation, occurs when the weight of the cargo causes the suspension system of the trailer to compress and decompress.
As the trailer becomes more heavily loaded, the suspension system compresses more, resulting in greater vertical oscillation. Conversely, if the trailer is nearly empty, there would be less weight to compress the suspension, leading to reduced vertical oscillation.
Therefore, based on the observation of the trailer bouncing up and down, it can be concluded that the trailer is more likely to be heavily loaded rather than nearly empty.