Prime mover (tractor unit)

Okay kiddo, have you ever seen a big truck on the highway? That big truck is made up of two parts - the trailer (the part that carries all the stuff) and the prime mover or tractor unit (the part that pulls the trailer). The prime mover is like the strongest kid in class who can effortlessly carry a heavy backpack for their friend.

The tractor unit is like the engine of the big truck. Just like how you need to pedal your bike to move forward, the prime mover needs fuel (usually diesel) to move the big truck forward. It also has a driver's cockpit where a grown-up sits and drives the truck.

The prime mover has a bunch of wheels that help it move smoothly down the road. These wheels are different sizes and are arranged in a special way to give the best possible grip on the road, like how you would put your feet in a certain way to balance on a tightrope.

Many different companies make prime movers, and they each have their own designs and special features. Some prime movers are really noisy and rattle a lot, while others are quiet and smooth like a magic carpet ride.

Overall, the prime mover is the powerful engine that pulls the trailer, and it's what makes those big trucks on the highway so impressive!