Inertia refers to the tendency of an object to resist any change in its motion. According to Newton's first law of motion, also known as the law of inertia, an object at rest will stay at rest, and an object in motion will continue to move at the same constant velocity in a straight line unless acted upon by an external force.

The physical quantity on which inertia depends is mass. Mass is a fundamental property of matter that measures its resistance to changes in motion.

The greater the mass of an object, the greater is its inertia, and as a result, the more force is required to accelerate or decelerate the object.

Objects with higher mass are more challenging to move from a state of rest or to stop when they are in motion.

Newton's second law of motion mathematically describes the relationship between inertia and mass:

```

F = ma

```

where:

* F is the net force acting on an object

* m is the mass of the object

* a is the acceleration of the object

As can be seen from the equation, the force (F) required to produce a specific acceleration (a) is directly proportional to the mass (m) of the object. This means that if an object has more mass, it requires a greater force to accelerate it to a specific speed. Conversely, an object with less mass will respond more readily to a given force, resulting in a greater acceleration.

In summary, inertia is a property of matter that resists changes in its motion and is directly related to the mass of the object. The more massive an object is, the greater its inertia and the more force is needed to alter its state of motion.