Final answer:
When a trailer is bouncing up and down slowly on a highway, it is more likely to be heavily loaded due to the higher center of gravity and uneven weight distribution. This causes vertical oscillation in the trailer.
Step-by-step explanation:
When a trailer of a freight truck is bouncing up and down slowly while driving on a highway, it is more likely that the trailer is heavily loaded. This bouncing motion is known as vertical oscillation, and it occurs when there is a high center of gravity or uneven weight distribution in the trailer.
In a heavily loaded trailer, the weight of the cargo creates a downward force, causing the suspension system to compress and the trailer to bounce. On the other hand, if the trailer is nearly empty, there is less weight to compress the suspension, resulting in less vertical oscillation.
Therefore, based on the observation of the trailer bouncing up and down slowly, it can be inferred that the trailer is heavily loaded.