A semi-trailer truck, also known as a tractor-trailer or a semi-truck, is a combination vehicle consisting of a tractor unit (also known as a cab or truck) and a semi-trailer. The tractor unit is responsible for providing the power to haul the semi-trailer, which is a trailer without a front axle. The semi-trailer is attached to the tractor unit using a fifth wheel hitch, which allows for the trailer to pivot and turn in relation to the tractor unit.

On the other hand, a full-trailer truck, also known as a straight truck or a box truck, is a truck that consists of a single unit with the cab and cargo area combined. Unlike a semi-trailer truck, a full-trailer truck does not have a separate tractor unit and trailer. Instead, the cab and cargo area are all part of the same vehicle.

The main difference between a semi-trailer truck and a full-trailer truck lies in their design and functionality. Here are some key differences between the two types of trucks:

1. Maneuverability: Semi-trailer trucks are more maneuverable than full-trailer trucks because the tractor unit and semi-trailer can pivot independently. This allows semi-trailer trucks to make tighter turns and navigate more easily in tight spaces. Full-trailer trucks, on the other hand, are limited in their maneuverability due to their one-piece design.

2. Weight capacity: Semi-trailer trucks typically have a higher weight capacity than full-trailer trucks. This is because the weight of the cargo is distributed between the tractor unit and the semi-trailer, allowing for heavier loads to be carried. Full-trailer trucks have a lower weight capacity because the entire weight of the cargo is concentrated in the cargo area of the truck.

3. Stability: Semi-trailer trucks are generally more stable than full-trailer trucks, especially when making sharp turns or traveling at high speeds. The weight distribution between the tractor unit and semi-trailer helps to maintain balance and stability. Full-trailer trucks may be more prone to tipping over or losing control due to their single-unit design.

4. Length: Semi-trailer trucks are typically longer than full-trailer trucks, as the tractor unit and semi-trailer are separate components. This allows for more flexibility in the length of the cargo being transported. Full-trailer trucks are shorter in length because the cab and cargo area are combined into a single unit.

In conclusion, while both semi-trailer trucks and full-trailer trucks are used for transporting goods, they differ in design, maneuverability, weight capacity, stability, and length. Each type of truck has its own advantages and disadvantages, depending on the specific needs of the transportation task at hand.