During ordinary conversations, Mass vs Weight is used interchangeably even though both terms are different. The mass of an object is the amount of material that an object contains and that is constant. On the other hand, weight is a measure of how the gravity force acts on that body. So, from the viewpoint of the definition of mass and weight, both are distinct. The application of mass and weight in the problems of engineering or physics is also different. In this article, we will find out the differences between mass and weight, i.e Mass vs Weight.
What is Mass?
In scientific or engineering contexts, the mass of a body is the measure of the amount of matter or stuff it contains. Mass is denoted using m or M. The unit of mass in SI unit systems is Kilogram (Kg) and in the FPS system is Pound (lb). As the amount of stuff or matter that the body is made of is always required to make that body, the mass remains constant in all places.
What is Weight?
Weight is the measure of the gravitational interaction between the objects having mass. It represents the amount of force acting on the mass due to gravitational acceleration. Weight is normally denoted by W and mathematically the weight of an object is defined as mass multiplied by the acceleration of gravity (g). So, mathematically,
Weight, W = m*g
As the gravitational acceleration, g varies with respect to the place where the object is, the weight of the object also varies. So, unlike the mass of an object, weight is not constant and the value of weight solely depends on the acceleration of gravity. Actually, weight varies proportionately with gravitational acceleration (As, m is constant, W ∝ g). It means the weight will be more if the value of gravitational acceleration is more and vice versa.
The unit of weight in SI unit systems in Newton (N) or Kg-m/s2 and the same in FPS unit system is Poundal or is lb-ft/s².
What are the differences between Mass and Weight?
In the following section, we will discuss the major differences between mass and weight.
1. Mass vs Weight: Definition
Mass is an inertial property of matter. It can never be zero (0). The mass always remains the same everywhere. On the other hand, As weight depends on the effect of gravity, it can be zero where no gravity is present like in space. Depending on the value of gravitational acceleration the magnitude of weight varies and it’s not constant.
Mass is an intrinsic property of matter. As weight is derived from the mass by multiplying with gravitational constant, mass is known as a base quantity and the weight is known as a derived quantity.
2. Mass vs Weight: Scaler or Vector
Mass is a scalar quantity. It has only magnitude and the direction does not affect it. Whereas, the weight of an object is a vector. Weight has magnitude and direction that is directed toward the center of the gravity well (Earth or other planets).
3. Mass vs Weight: Impact of Location
The weight changes with respect to the location of the object as gravitational acceleration changes. Various factors affect the acceleration due to gravity like:
- With an increase in the distance between the body and the center of the planet, the magnitude of gravitational force reduces.
- As the earth is not uniformly spherical throughout, the gravity varies with respect to the location of the object on the Earth
- Also, the force of gravity is weaker at the equator due to centrifugal forces produced by the planet’s rotation.
- Each planet has its own gravitational acceleration values. So, it varies from one planet to the other.
Due to the above factors, the weight of any object is not constant and varies. During, the free-falling situation in space, weight is assumed to be zero. But, the mass of the body does not get affected by the location change.
4. Weight vs Mass: Measurement
Mass is measured by using an ordinary balance. The basic principle of measuring mass using balance is to compare the unknown mass with known values of mass. Balance works fine in all places because the effect of gravity will provide the same effect on both the unknown and known mass. So, the gravitational effect will be insignificant and mass can be easily measured.
But the weight of an object is measured by using a spring balance.
5. Mass vs Weight: Units
As already stated earlier, the units of both mass and weight are different. Mass is usually measured in gram or kilogram whereas the weight is measured in newton which is a unit of force.
6. Mass vs Weight: Examples
Sometimes, people use weight to mean mass because, on Earth, it is assumed that the force of gravity is constant. But, an object with a mass of 10 Kg weighs approximately 98.1 newtons on the Earth’s surface. This is obtained by multiplying the mass (10 kg) by the gravitational field strength (9.81 m/s2). The weight of the same object will be less on Mars as the gravity is weaker, and more on Saturn or Jupiter. But the mass of that object will always be the same 10 Kg.