# Basic Physics lesson-4 : Mass and Weight.

Umesh is a freelance writer contributing his creative writings on varied subjects in various sites and portals in the internet.

## Introduction

There are many concepts in basic Physics that make a rudimentary understanding of the science to the students. In our earlier articles on Distance and displacement, Speed and velocity, and Acceleration, we learned about displacement, velocity, and acceleration which were related to the motion of the bodies. Now in the present lesson, we would like to understand and learn the most basic concepts regarding the physical entities known as mass and weight.

## What do we understand by mass?

Mass is the amount of matter in the body. It has a unit of gram or kilogram (1 kilogram=1000 gram) or ounce or pound (1 pound=16 ounce). There are many other units of mass to denote small as well as bigger masses. For example, 1 milligram means one-thousandth of a gram while 1 quintal means 100 kilograms.

If you go to market and buy 300 grams of chocolate and find it consisting of only 10 pieces as against your requirement of 20 then you would have to buy 300 grams more. So, here the amount of material is doubled. So, mass is an inherent characteristic of matter. So when we specify a quantity as 100 grams it signifies a fixed mass of 100 grams not more and not less. One interesting thing about mass is that one can not tell the mass just by the appearance of an item. 100 grams of cotton or wool would look much bigger when compared to the 100 grams of an iron piece.

## What do we understand by weight?

Many people get confused between mass and weight. They use both the terms interchangeably. For understanding the difference between the two we have to understand the acceleration due to gravity on our planet Earth. What happens is that when we drop a thing from a height it gains velocity because Earth attracts it by its gravitational force. It then strikes the ground with increased velocity and comes to rest. The acceleration during this downward journey is known as acceleration due to gravity and is denoted by the letter g. Let us see what happens when we throw a thing upwards. The Earth attracts it downwards and it gets deaccelerated and stops after reaching a height and comes backwards. This deacceleration is also caused by Earth's gravitational field. The acceleration due to gravity at the surface of the Earth is about 9.8 metres per second2 and is the same for everybody whether having less or more mass.

Weight is the force with which a body gets attracted to the Earth. So, weight is defined as the multiplication of mass with acceleration due to gravity (g). Hence, we can say that 1 kg weight = 1 kg mass x 9.8 meters per second2. For sake of simplicity 1 kg meter per second2 is represented by 1 Newton. So, finally, we get 1 kg weight = 9.8 Newton. Remember that weight is a force and 1 kg weight is nothing but 9.8 Newton. In our practical life we do not use Newton in day to day conversation and simply say so much kg of weight. In speaking we even omit the world weight and say so much kg.

## Examples

Mass and weight are different and we can understand it by an interesting example. Let us consider the Moon where the acceleration due to its gravity is about one-sixth of that of Earth. What would happen to the weight of a body on the Moon? It would be one-sixth of that on Earth. What will happen to the mass? It would remain the same as the material in the body is the same. Different planets in our solar system have different gravitational forces and accordingly, the same mass would have different weights there. Just imagine that we would be 25 times heavier on the planet Jupiter! It is obvious that we would not be able to walk on Jupiter!

## Weightlessness

Weightlessness is an interesting thing to know. What happens when a person goes to a place where there is no gravity? For example a place far from Earth in the void of space. What would be our weight there? It would be zero. So we would be in a state of weightlessness there and would freely float in the space. Astronauts feel it when they go into space. Even on Earth in some laboratories, an artificial weightless environment is created to train the Astronauts.

How do we move when we are in a state of weightlessness? We have to use a propellent firing system so that when we fire it in one direction the recoil or reaction would move us in opposite direction. Have you seen in movies persons flying in the air opposite to some firing exhaust mechanism at their back? That is what is meant by the reaction of that firing on them.

## Conclusion

In essence, mass is the amount of matter in a body while weight is the force with which the Earth attracts it. As laymen, we use both the words interchangeably but in Physics they have entirely different meanings to be remembered as 1 kg weight = 9.8 Newton force.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

Umesh Chandra Bhatt (author) from Kharghar, Navi Mumbai, India on June 25, 2020:

SKMUNSHI, thanks a lot. Appreciate.

SKMUNSHI on June 25, 2020:

The concept of mass and weight has been nicely introdued in this write up alng with the concept of varying acceleration due to gravity in different planets& and its effect on weigt .The resulting concept of weightlessness and its effect is also covered.Thus the author has intoduced one of the most important

Umesh Chandra Bhatt (author) from Kharghar, Navi Mumbai, India on March 09, 2020:

Anurag, thanks for your nice comment.

Scroll to Continue

Anurag on March 09, 2020:

Another interesting and insightful article!!!

Hope it must have cleared the common confusion regarding the mass and weight to all young learners!!!

Keep posting new!!

Umesh Chandra Bhatt (author) from Kharghar, Navi Mumbai, India on March 06, 2020:

DreamerMeg, thanks for the interest shown for this lesson. Appreciate much.

Umesh Chandra Bhatt (author) from Kharghar, Navi Mumbai, India on March 06, 2020:

Eric, thanks for your encouraging words. Highly appreciate.

DreamerMeg from Northern Ireland on March 06, 2020:

I remember doing mass and weight but not the multiplication to produce Newtons. Interesting. Thanks

Eric Dierker from Spring Valley, CA. U.S.A. on March 06, 2020:

Really interesting and well done. I sure learned a lot here. Weight becomes simply a relative factor. Cool.

Umesh Chandra Bhatt (author) from Kharghar, Navi Mumbai, India on March 06, 2020:

Singh Sahib, thanks a lot for your nice comment. Happy to know that you are also a Physics PG. I did it in 1972. What about you?

MG Singh emge from Singapore on March 06, 2020:

I completed a PG degree in physics and it was nice reading your article.

Umesh Chandra Bhatt (author) from Kharghar, Navi Mumbai, India on March 06, 2020:

Cheryl, thanks for your visit and comment. Highly appreciate.

Cheryl E Preston from Roanoke on March 05, 2020:

Thanks for the physics lesson. Very informative.