We all were introduced to these terms when we were in school. They play a significant role in the laws of physics and help us to solve various problems. There are many equations in physics that use these terms. However, these terms do sound different but many of us think them as the same thing. So we are going to find out now what is the difference between weight and mass.


It can be defined as the amount of matter present in an object. However, this definition is not so accurate. Therefore mass is defined in terms of inertia.

Inertia is a resistance that opposes the change in the state of motion of an object or when an object is at rest. The unit of mass is the kilogram (Kg). There is one basic difference between a mass and weight which is a mass remains unchanged regardless of its position in the space and weight of an object changes with space.

According to the universal law mentioned above, the two masses attract each other with the force proportional to it. But contrarily to that, there is no effect of force on the magnitude of the mass i.e. a person having a mass of 100kg will have the same mass of 100 kg on other planets as well.


It can be defined as the force that is being exerted by the gravity on a body of a certain mass. Weight is also a force, therefore its unit is also the same as of force i.e. Newton (N). In other terms, we can say that weight is the force that our mass exerts on the earth. 

newtons law of universal gravitation.

F= GxM1xM2/ R

In this formula, G is constant.

M1 is mass of object one (suppose it you)

M2 is mass of object two (suppose it earth)

R is the distance between two objects.

This formula is called Newton’s law of universal gravitation. It states that every other particle in the universe exerts a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

On putting the values and solving the above-mentioned equation we get

, F= 9.8 M1 

This means, acceleration due to gravity=9.8 m/s.

 The above equation has reduced the universal gravitational law to Newton’s second law of motion: F=ma.

The above-mentioned equation shows that an object falls towards the earth with an acceleration of 9.8 meters per second square. The magnitude of acceleration in different planets is different. The acceleration due to gravity on the moon is 1/6th of the earth gravity i.e. 1.620 meters per second square.

Therefore, an astronaut of mass 100 kg will weigh 100×9.8= 980 Newton on earth, but the same astronaut will weigh 100×1.620= 162 Newton on the moon.

Relation between mass and weight

The mass of an object can be measured by a weighing scale. It measures the opposite force that the earth exerts on an object in response to the force that the object exerts on it. A weighing machine measures the normal force exerted by earth and divides it by 9.8 which gives us the approximation of our mass.

Moreover, a weighing machine calibrated to the earth’s gravity will give the wrong result on other planets. This system fails to work correctly when it is in free fall because the weighing scale and an object both fall at the same speed. This doesn’t allow any normal force to act on the body. Similarly, when an object is placed in the space the weighing system would not show any deflection in its needle because of no normal force.

Mass can be measured using an instrument called beam balance. This system uses a known magnitude of mass to determine the mass of an unknown object.

Now we can say that mass weight are two different terms but they have their nexus. These terms are also used in many other fields apart from physics. Great discoveries have been made on the basis of these two terms and there will be more of them in the future too.

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