The mass of an object is equal to the sum of the masses of its parts. This is a fundamental principle of physics, known as the law of conservation of mass. It states that the total mass of a closed system remains constant over time, regardless of the changes that occur within the system.

Examples:

Consider a simple example of an object made up of two identical parts. If each part has a mass of 1 kilogram, then the total mass of the object will be 2 kilograms. This is because the mass of the whole is equal to the sum of the masses of its parts.

Similarly, if you have a car with a mass of 1000 kilograms, and you add a 10-kilogram suitcase to the trunk, the total mass of the car will increase to 1010 kilograms. This is because the mass of the suitcase is added to the mass of the car, resulting in an increase in the total mass.

In short, the mass of an object is always equal to the sum of the masses of its parts, regardless of the nature or composition of the object.