Difference Between Mass and Weight

Mass and weight are two terms that are often used interchangeably in everyday life. Many people speak of the mass of an object as its weight and the weight to refer to the mass. But these concepts are very different and then we will see what those differences are between the two.  Difference Between Mass and Weight

DOUGH  Difference Between Mass and Weight

Mass is the amount of matter that an object has. It is divided into two types: inertial mass and gravitational mass. The most common type used in physics is inertial mass, which is a quantitative measure of an object’s resistance to acceleration. On the other hand, gravitational mass is a measure of the magnitude of the attractive force that is exerted on a given object.

In the International System of Units, the unit used to measure mass is the kilogram (kg), while in other systems pounds (lb.) and grams (g) are also used to refer to mass.

Mass should not be confused with the amount of a substance. Matter and energy may well be two different forms of mass. According to Einstein’s Theory of Relativity, electromagnetic waves also have mass. According to this theory, there are two types of mass: the rest mass and the relativistic mass. According to this same theory, the mass of an object does not always remain constant. The rest mass, as its name implies; is the mass of an object at rest, while relativistic mass refers to the mass of the object when it is in motion.


Weight refers to the measure of the force of gravity on an object. This differs constantly, since the force of gravity is not the same everywhere (the weight of a person is not the same on Earth and on the Moon. Example: a person with a mass of 50 kg and a weight of 491 newtons in Earth; on the Moon it will have the same mass, but will only weigh 81.5 newtons).

Generally, weight is measured in  newtons  (N), not (kg). Simply put, weight is the gravitational force acting on a body, while mass is the intrinsic property that does not change.

The formula to calculate the weight of a substance is P = M * G: Weight equals mass times gravity.

The concept of weight was developed from the Laws of Motion and Newton’s Law of Universal Gravitation.

There are machines that can measure our mass and others that can measure our weight. The machines we see in doctors’ offices that use a balance scale to measure our “weight”; actually what they measure is our mass.

Now, there are machines in which people stand still for a moment and at the end their true weight (in newtons) appears on a screen.

Key differences between weight and mass

  • Weight can vary, but mass is constant.
  • Second one  is measured in kilograms (kg), while first one is measured in newtons (N).
  • Second one refers to the amount of matter that an object has, but second one refers to the force of gravity acting on an object.

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