Difference between Mass and Weight

What is the difference between Mass and Weight?

What is the meaning of the sentence when someone says “His weight is 40 kg?”

The term ‘weight’ is commonly used to describe the amount of matter that is contained in an object or a person. Though conventionally correct, seen technically, this description is very wrong! The given definition can be used to define the mass of any object or person but not weight.
What, then, does weight actually mean?

Let us start from scratch and see what does mass and weight mean individually.

What is Mass?

It defines the amount of matter in the object.

What is Weight?

It defines the amount of force exerted by the gravitational force on the object.

Given the definitions of weight and mass, we can extract the differences between mass and weight.

Mass is the basic property of a matter whereas weight defines the force with which the mass of an object is pulled down due to gravity.

Let us imagine we take a trip to moon. What do you think your weight and mass would be on moon? The mass never changes with place, but weight does. Hence, on moon, your mass would be the same as that on earth whereas your weight would differ as according to the gravitational pull exerted by the given planet.

Mass is a scalar quantity whereas weight is a vector quantity. Now, what exactly does scalar and vector mean?

What is Scalar?

The quantities which describe only the numerical value of a given force are known as scalar quantities. The example, as given above, is mass. More examples include speed, time temperature and such.

What is Vector?

The quantities which describe the direction along with the numerical value of a given force are known as vector quantities. The examples of vector quantities are weight, velocity, acceleration and many more.

Units of Mass and Weight

• Mass : The unit of mass is Kilogram(Kg).
• Weight : The unit of weight is Newton(N).

Mathematically, the weight of an object is equal to the mass of that object multiplied by the gravitational force.

W=mg

where W is the weight, m denotes the mass and g is the universal acceleration of gravity or in simpler terms, Gravity.

These two quantities do not even have the same units of measurement! How can they be same? In conclusion, both the quantities are different but not independent from each other.

Activity :
The mass of a laptop on earth is 2 kg, and the constant gravitational force is 9.8 m/s2, what is the weight of the laptop.

Answer : w = mg
=(2 kg)* (9.8 m/s2)
=19.6 N

Branches of Physics (Free Lecture)

Newton’s Laws of Motion

Motion in Physics

Motion is one of the major topics in physics. It is a part of mechanics. Scientists have set different laws or rules which explain motion and the causes of changes in motion.

Mathematical Principles of Natural Philosophy

The most famous laws of motion were formulated by Sir Issac Newton. The three laws of motion were compiled by him in Mathematical Principles of Natural Philosophy (published in 1687) His laws of motion are three physical laws which actually laid the foundation for classical mechanics. Scientists have used certain basic terms to describe motion.

Terms used to describe motion

Force: It is required to act on an object to move it or to change its motion.
Velocity: It is also known as speed .Velocity of an object is influenced by forces.
Acceleration: It is a measure of how much the velocity of an object changes in a certain time (one second).
Mass: It is the amount of something present and is measured in grams or kilograms.

What are the three laws of motion?

1. Newton’s first law of motion

Every object in a state of motion tends to remain in that state of motion unless an external force is applied to it. This is also known as Law of inertia.

2. Newton’s second law of motion

The relationship between an object’s mass m, its acceleration a, and the applied force F is F = ma. Acceleration and force are vectors. In this law the direction of the force vector is the same as the direction of the acceleration vector. This law defines how velocities change when forces are applied.

3. Newton’s third law of motion

For every action there is an equal and opposite reaction. This happens in a situation such as if we step off a boat onto the bank of a lake. As one move in the direction of the shore, the boat tends to move in the opposite direction. If not careful, the person may fall.

Laws of motion facts

The three laws of motion are verified over years by experiments and observations. They are found to be excellent approximations at the scales and speeds of everyday life. However, these are inappropriate for use at very small scales, very high speed and strong gravitational fields.