[Physics Class Notes] on Mass and Weight Pdf for Exam

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.

The mass has a magnitude that is usually measured in kilograms and grams. 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 to the body.

Therefore, the 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

The weight is the amount that something weighs. 

It is defined as the force that acts at all times on the objects near 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

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.

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 the symbol kg.

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

Mass vs Weight

Do You know?

Some interesting facts about mass and weight are:

• 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.