Mass and Weight - Definition, Relation, FAQs

What is Mass?

Mass is defined as the amount of matter present in an object. It is a fundamental property that does not change regardless of the location in the universe. The greater the mass of an object, the more matter it possesses.

The S.I. Unit of mass is Kilogram (Kg).

Role in Physics: Mass is a fundamental property of matter and appears in Newton's Second Law of Motion and momentum, $F=m a$,

where,

• $F$ is force
• $m$ is mass
• $a$ is acceleration.

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Types of Mass

Mass can be categorized into two types:

1. Inertial Mass: Measures an object's resistance to acceleration when a force is applied.
2. Gravitational Mass: Determines the strength of the gravitational force exerted by or on the object.

What is Weight?

The force exerted on an object due to gravity is called the Weight of an object. It is a vector quantity meaning it has both magnitude and direction. It changes with the strength of the gravitational field. Unit of Weight is the newton (N), as it is a measure of force.

For example, an object weighs less on the Moon than on Earth because the Moon's gravity is weaker.

Formula to Calculate Weight

$$
W=m g
$$

where $W$ is weight, $m$ is mass, and $g$ is the acceleration due to gravity (approximately $9.8 \mathrm{~m} / \mathrm{s}^2$ on Earth).

Relation Between Mass and Weight

The weight ( $W$ ) of an object is directly proportional to its mass $(m)$ and the acceleration due to gravity $(g)$. The formula is:

$$
W=m g
$$

where $W$ is weight, $m$ is mass, and $g$ is the acceleration due to gravity (approximately $9.8 \mathrm{~m} / \mathrm{s}^2$ on Earth).

Difference Between Mass and Weight

The below table shows the difference between the Mass and Weight along with their properties:

Can Weight Change Without a Change in Mass?

Yes, weight can change even when mass remains the same. Mass is the amount of matter present in an object and does not depend on location. However, weight is the force with which gravity pulls an object toward the Earth or any other celestial body.

The relationship between mass and weight is given by the formula:
Weight = Mass × Acceleration due to Gravity (g)

Since the value of gravity (g) varies from place to place, weight also changes. For example, a person weighs less on the Moon than on the Earth because the Moon’s gravity is weaker, even though the person’s mass remains unchanged. Similarly, weight can vary slightly at different altitudes on Earth.

Can a Body Have Mass but No Weight?

Yes, a body can have mass but no weight. Mass is a constant property of an object and does not depend on gravity. Weight depends on gravitational force, so when gravity is absent or negligible—such as in outer space or during free fall the weight becomes zero while the mass remains unchanged.