Inertia and its significance:
Inertia is the resistance of an object to changes in its state of motion. It is directly related to an object's mass, with greater mass resulting in greater inertia. Inertia plays a crucial role in determining how objects behave when forces are applied to them. The higher the inertia, the more difficult it is to change the object's motion.

Comparing the inertia of different objects:
To determine which of the given options has the least inertia, let's analyze the characteristics of each object and consider their masses.

1. Pencil:
A pencil is a lightweight object with a small mass. It consists primarily of wood and a graphite core. Due to its small mass, a pencil has relatively low inertia compared to heavier objects.

2. Car:
A car is significantly heavier than a pencil and consists of various components such as metal, engine, and other mechanical parts. Cars have a higher mass, resulting in greater inertia than a pencil.

3. Train:
Trains are much larger and heavier than cars. They consist of multiple connected cars, an engine, and additional equipment. The mass of a train is significantly higher compared to both a pencil and a car. Therefore, trains have greater inertia than cars and pencils.

4. Truck:
Trucks are even larger and heavier than trains. They are designed for carrying heavy loads and have a substantial mass due to their size and construction. Consequently, trucks have the highest inertia among the given options.

Conclusion:
Comparing the inertia of the given objects, we can conclude that the pencil has the least inertia. It is lightweight and has a small mass compared to the car, train, and truck. Inertia increases with mass, so as the mass of an object increases, so does its inertia. Therefore, the truck has the highest inertia among the options provided.

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