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Difference between Mass and Weight

Physics | 7-14 yrs | Reading Pod, Interactive

What is the difference between Mass and Weight?

What is the meaning of the sentence when someone says “His weight is 40 kg?”

The term ‘weight’ is commonly used to describe the amount of matter that is contained in an object or a person. Though conventionally correct, seen technically, this description is very wrong! The given definition can be used to define the mass of any object or person but not weight.
What, then, does weight actually mean?

Let us start from scratch and see what does mass and weight mean individually.

What is Mass?

It defines the amount of matter in the object.

What is Weight?

It defines the amount of force exerted by the gravitational force on the object.

Given the definitions of weight and mass, we can extract the differences between mass and weight.

Mass is the basic property of a matter whereas weight defines the force with which the mass of an object is pulled down due to gravity.

Let us imagine we take a trip to moon. What do you think your weight and mass would be on moon? The mass never changes with place, but weight does. Hence, on moon, your mass would be the same as that on earth whereas your weight would differ as according to the gravitational pull exerted by the given planet.

Mass is a scalar quantity whereas weight is a vector quantity. Now, what exactly does scalar and vector mean?

What is Scalar?

The quantities which describe only the numerical value of a given force are known as scalar quantities. The example, as given above, is mass. More examples include speed, time temperature and such.

What is Vector?

The quantities which describe the direction along with the numerical value of a given force are known as vector quantities. The examples of vector quantities are weight, velocity, acceleration and many more.

Units of Mass and Weight

  • Mass : The unit of mass is Kilogram(Kg).
  • Weight : The unit of weight is Newton(N).

Mathematically, the weight of an object is equal to the mass of that object multiplied by the gravitational force.


where W is the weight, m denotes the mass and g is the universal acceleration of gravity or in simpler terms, Gravity.

These two quantities do not even have the same units of measurement! How can they be same? In conclusion, both the quantities are different but not independent from each other.

Activity :
The mass of a laptop on earth is 2 kg, and the constant gravitational force is 9.8 m/s2, what is the weight of the laptop.

Answer : w = mg
=(2 kg)* (9.8 m/s2)
=19.6 N