The concept of inertia is a fundamental concept in physics. It is defined as the tendency of an object to resist changes in its state of motion. In other words, it is the property of an object that causes it to remain at rest or in motion with a constant velocity unless acted upon by an external force. The correct option among the given options is option D, which states that inertia is directly proportional to the mass of an object.

Explanation:

Direct Proportionality to Mass:

Inertia is directly proportional to the mass of an object. This means that the greater the mass of an object, the greater its inertia. This can be explained using Newton's first law of motion, which states that an object at rest will remain at rest, and an object in motion will continue in motion with a constant velocity unless acted upon by an external force.

For example, consider a small ball and a large ball. If we push both balls with the same force, the small ball will move faster than the large ball because it has less mass. This is because the large ball has more inertia, and it requires more force to put it in motion.

The Importance of Inertia:

Inertia is an important concept in physics, and it has many practical applications. For example, it is the reason why seat belts are important in cars. When a car suddenly stops, the passengers continue to move forward due to their inertia. The seat belt applies an external force that stops the passengers from moving forward and prevents injuries.

Conclusion:

In conclusion, inertia is the tendency of an object to resist changes in its state of motion. It is directly proportional to the mass of an object. The greater the mass of an object, the greater its inertia. Inertia has many practical applications in everyday life and is a fundamental concept in physics.