Mass and Weight

What is Mass?

Mass is the fundamental attribute of any physical body.

All the objects have a matter inside them and the measurement of the matter is the mass. 

The total mass of the system is assumed to be constant. This means that the mass remains unaffected by the gravitational field strength, regardless of the location, the object or person is in.

Mass has a magnitude that is usually measured in kilogram and gram. Therefore, it is a scalar quantity.

We are on earth and we measure things on earth with earth's gravity.

If your weight is 70 kg which means you weigh 70 kg and the scale would read it 70kg or 154 lbs.


Mass Definition

Mass is defined as the measure of the matter inside a body.

In physics, mass is a quantitative measurement of inertia.

Let’s understand the concept of mass by understanding Newton's second law.

For example, a body of mass, ‘m’ is moving with an acceleration ‘a.’ The force, ‘F’ is applied to the body given by,

                                F = m . a

Here, mass is a measure of its resistance to acceleration when a force is applied on to the body.

Therefore, greater the mass of a body, the minimum change produced by an applied force.


Mass Meaning

Mass is referred to as the amount of matter contained in a body.

For example, a human body has bones, muscles, tissues, RBC, WBC. As combined, they form a body’s mass.

A person or object may be weightless on the moon because of lack of gravity while he maintains the same mass at all places without considering his location.


Weight Definition

Basically, the weight is the amount that something weighs. 

It is defined as the force that acts at all times on the objects near to the earth’s surface.

In the field of science and engineering, the weight of an object is related to the force acting on that object, either due to gravity or due to a reaction force that holds it in a place. 

In simple terms, it is the force with which a body is pulled towards the earth.

Therefore, weight is the measure of the heaviness of an object.


Relationship Between Mass and Weight

Weight is defined as the force of gravity with which a body is attracted to Earth or another celestial body, and is equal to the product of the object's mass, and the acceleration of gravity given by,

                                    W =  F = mg

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The above equation is applicable at all times even when the object is not accelerating. This means the object is under free-fall and no external force other than gravity is acting upon it. 

Here, W is the weight of the body

F = external force

m  = mass of the body

g  = acceleration due to gravity

Here, g is the measure of the intensity of the gravity field in N/kg at any location.

For example, if I weigh 24 kg on earth,  then my mass on the moon will be 1/ 6 to the weight on the earth i.e., 4 kg on the moon.

The mass on the Moon is less than the Earth. However, its gravity is less than the Earth.

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Unit of Mass and Weight

In physics, each object has a unit that determines the standard measurement of that body. 

Therefore, a physical quantity such as mass also has a unit. In International systems, SI, the mass is measured in Kilograms denoted by symbol kg.

Here, weight is a vector quantity measured in Newton, symbolized by N.


Mass vs Weight

Mass 

Weight 

Mass is an attribute referring to the amount of material inside the body.

Weight is the force exerted by gravity on an object (force is caused by gravity pull on the body).

Represented by, ‘m.’

Represented by, ‘mg.’

A scalar quantity (has a magnitude only).

 

A vector quantity (has magnitude and direction) that is directed towards the center of earth.

Constant regardless of gravitational field strength.

Varies according to gravitational field strength. 

Mass remains constant at all locations.

Mass increases or decreases with higher or lower gravity.

Mass can never be zero.

Weight can be zero, if the body is in a place with no gravity, such as in space.

Usually measured by analytical balance,  beam balance or calibrated electronic balance.

Measured by spring or compression balance.

Measured in kg or g.

Often measured in Newton (as it is defined as the force of gravity).


Do you know?

The mass does not remain constant.

Nuclear reaction: In this reaction, a tiny amount of matter is converted into a large amount of energy, this reduces the mass of the substance.

FAQ (Frequently Asked Questions)

Q1: Can Mass be Created?

Ans: Mass can neither be created nor be destroyed. However, it can be changed from one form to another form. For instance, the mass of reactants in a chemical reaction is equal to the mass of products so formed.

Q2: How Does Volume Affect the Mass?

Ans: No effect.

If the volume increases, the mass still remains constant. 

For example, I have a metal of mass 3 gms. The atoms inside this metal are tightly bound and the volume of each atom is just two cubic centimeters. Now if I heat  this metal, the volume of each atom expands to 3 cubic centimeters while the mass remains unchanged i.e., 3 gms.

Q3: Do Photons have Mass?

Ans: Light is made of small packets called photons that are massless particles. 

As confirmed experimentally, photons have energy and momentum but don’t have mass.

Q4: What is a Relativistic Mass?

Ans: Relativistic mass is a special theory.of relativity. 

This theory is applied to the objects in motion. The corresponding formulas for the theory are: p = mv and  E = mc2. This relativistic mass becomes infinite (because of infinite kinetic energy) when velocity of the body approaches the speed of light i.e., c.