What is Mass

Mass is a term well-defined in physics. Basically, it defines the amount of matter present in a substance. It is a dimensionless quantity, and does not take into consideration gravity, while being calculated. In easier words, mass would be matter of an object which when present in a gravitational field, would have weight. According to Newton, it is measured by the extent to which an object resists change when it is subjected to force.

Is Mass the Same as Weight?
It is important to remember that these two terms are different and cannot be interchanged randomly. As stated by Newton it is the extent to which an object resists a change in direction or motion. According to this mass can be determined using the following formula,


Where, F is the force applied to the object, m is the mass of an object and a is the acceleration that results when the object is set into motion. Weight will be defined only when an object with a particular or specific mass is placed in a field of acceleration such as the gravitational field. The major difference between the two terms is that, weight is a vector whereas mass is a scalar quantity. A vector is a quantity that is defined by magnitude and direction, whereas a scalar quantity is something that remains unaltered on a co-ordinate system. For example, the weight of an object being a vector quantity would vary on the surface of earth, the moon, or some other planet. This is because the gravitational field differs on each of these surfaces. But, the mass of the object would not change. Which brings us to the question, is mass a physical property? Of course it is, though it doesn't describe the state but it is the matter of an object which is a physical quantity, thus making it a physical property as well.

Measurement of Mass
It is measured in grams or kilograms according to the SI system. There are various other units in which it could be measured, such as pound, tons, atomic mass unit.

Mass is a physical quantity that remains conserved and does not change with time. The law of conservation of mass is just like the law of conservation of energy, it too cannot be created nor destroyed. All types have energy have some mass associated with it. This gets added to systems when energy is added to them. It is subtracted when the energy leaves a particular system. Thus the total mass will always remain the same just like energy. The simplest way to associate mass with weight is by multiplying it by the gravitational field strength; given by the following formula;


Here, W= weight, m = mass and g = strength of the gravitational field which is approximately 9.8 meters/sec².

Formulae for Mass
In the earlier sections, I have mentioned the determination of mass using Newton's concept. The next few formulae are used to determine it using various other parameters.

• p = mv; where p is the momentum, m is the mass, v is the velocity
• E = ½ mv², where E is the kinetic energy, m is the mass and v is the volume
• E = mc², here c stands for the velocity of light.
• Density = Mass/ Volume

All these formulae must have given you the idea of how important mass is in determining any given parameter in physics. Hope this article has helped you understand about it and how is it different from its vector counterpart 'weight'.