Mass

From Newton to Einstein, the history of one of the basic building blocks of the physical universe – the Mass – has influenced the manner in which we learn science today. Whether it is classical mechanics or nuclear physics, mass is the foundation of how we perceive matter and the universe. So, let's dive into this simple yet most fundamental unit of science!

1.0What is Mass? 

Mass is the amount of matter present in an object which remains constant regardless of its colour, shape, and location where it is placed. It is a scalar quantity, meaning it only has magnitude and no direction. The SI unit of mass is the Kilogram, with other imperial units being tonne, milligram (mg), quintal, etc. 

Note that mass is an intrinsic property of matter, meaning that it does not change with temperature, pressure, or gravity. Meaning if an object weighs 30 kg on Earth, it will weigh the same under the water or on the Moon, Mars, or anywhere in the universe. 

2.0Law of Conservation of Mass: 

• Proposed by Antoine Lavoisier in 1789, the law of conservation of mass explains the reason why mass remains unchanged with physical or chemical change in a system. According to this law: 
• Mass can neither be created nor destroyed in a chemical or physical change; it can only change form. 
• In chemistry, the law states the feature of a chemical reaction in a closed system as the total mass of reactants = the total mass of products. 

3.0Mass, Inertia, and Force: 

The mass of a body is the measure of its inertia, the natural tendency of a body to resist any change in motion or rest. A heavier body (greater mass) has more inertia and therefore requires a greater force to move it compared to a lighter body (lesser mass). 

This relation between Mass, Inertia, and Force was discovered by Newton, and he expressed it in his second law of motion by this famous formula:  

F = ma 

This law also explains why bodies with lower mass accelerate more at a certain force than bodies with a higher mass. 

4.0Mass-Energy Relation: 

The mass-energy relation is an extension of the law of conservation of mass. That is, although the law is valid for all physical and chemical changes, there seems to be some energy loss in reactions of larger energy production, like nuclear fission or fusion. 

So, in 1905, Albert Einstein gave one of the most groundbreaking theories of modern physics, the Special Theory of Relativity. In this, he showed that mass and energy are interconvertible, and the mass that seemed to be lost got converted into energy. This, he expressed mathematically in the famous equation: 

Here, 

• E is the energy 
• m is the mass in kilograms 
• c is the speed of light (3 × 10⁸) 

In the equation, the value of c² is very large, which shows that even a small amount of mass can give away a huge amount of energy, which exactly happens in nuclear fission, fusion, atomic bombs, and nuclear power plants. 

5.0What is Weight? 

Weight is the force with which a body is accelerated by the gravity of a planet or celestial body towards its centre. In other words, weight is the gravitational force acting upon a body of a certain mass. Weight is a vector quantity, meaning it has both magnitude and direction. It has the SI unit Newton (N). The Weight of a body can be related to the mass of a body as: 

W = mg

Here, 

• W is the weight 
• m is the mass 
• g is the acceleration due to gravity 

Since the value of g varies depending on various factors, the weight of the body also changes with a change in g. For example, a person feels lighter at the equator compared to the pole. This is because the value of g is less at the equator than at the poles of Earth. 

Similarly, the gravity of the moon is ⅙ th of the Earth's, due to which the weight of a person becomes ⅙ th of his actual weight on Earth. 

6.0Difference Between Mass and Weight: 

Mass and Weight may look similar, but they are not and here are the reasons why:

7.0Mass and Weight beyond Gravity: 

When we think of mass and weight, we think of them in everyday experiences on Earth. But what if the body is taken beyond gravity in Space? We know that mass remains constant in every gravitational pull, but what about zero g? Will the mass be constant at zero g as well? The answer to this question is yes, the mass of the body never changes, whether they are on a planet under the gravitational pull or in space where the gravity is zero. This makes calculations related to mass easier for astronauts in space. 

However, this is not the case with weight. Unlike mass, in the absence of gravity or zero g, the weight of a person or object becomes zero or negligible, which lets them experience weightlessness. This is why in the International Space Station, where the body always remains in free fall, the body of the astronaut feels weightlessness, making them float around in the spaceship.