The inertia of an object is measured by its ______.

mass

The correct answer is option 3. mass.

Inertia is a fundamental property of matter that describes its resistance to changes in motion. Objects tend to maintain their current state of motion, whether at rest or in uniform motion, unless acted upon by an external force. The greater the inertia of an object, the more resistant it is to changes in its motion.

Mass is the measurement of the amount of matter in an object. It quantifies the inertia of the object. The relationship between mass and inertia is described by Newton's First Law of Motion, which states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.

According to Newton's First Law, an object with no net external force acting on it will maintain its state of rest or uniform motion. This law emphasizes the concept of inertia, where objects resist changes in their motion. The magnitude of this resistance depends on the mass of the object.

When an external force is applied to an object, it causes the object to accelerate. The greater the mass of the object, the more force is required to produce a given acceleration. This demonstrates how mass quantifies the inertia of the object—it reflects the object's resistance to changes in its state of motion.

Mass also plays a crucial role in determining the gravitational force experienced by an object. According to Newton's Law of Universal Gravitation, the gravitational force between two objects is directly proportional to the product of their masses. Thus, mass not only quantifies inertia but also influences the gravitational interactions between objects.

Mass is typically measured using standard units such as kilograms (kg) or grams (g). It can be determined experimentally using various methods, including balances and scales.

In summary, mass is the measurement used to quantify the inertia of an object. It reflects the object's resistance to changes in its motion and plays a fundamental role in describing its behavior according to Newton's laws of motion. Therefore, inertia is measured by the mass of an object.