The SI unit of Inertia is

In physics, mass is used to quantify inertia because the greater the mass of an object, the more it resists changes to its motion. The SI unit of inertia is, therefore, the same as the SI unit of mass, which is kilogram (kg).

Explanation:

1. Definition of Inertia:
   Inertia is the tendency of an object to remain at rest or in uniform motion unless acted upon by an external force. This property is directly related to the object's mass.
2. Role of Mass in Inertia:
   Mass reflects how much matter is in an object and determines its resistance to acceleration when a force is applied. For example:
   • A heavier object (more mass) has higher inertia.
   • A lighter object (less mass) has lower inertia.
3. SI Unit of Inertia:
   Since inertia is directly linked to mass, the SI unit of inertia is the kilogram (kg).

Example:

• A car with a mass of 1,000 kg has higher inertia than a bicycle with a mass of 15 kg. This is why it is harder to stop or change the motion of a car compared to a bicycle.

Final Answer:

The SI unit of inertia is kilogram (kg) because mass quantifies inertia.