An Introduction
We presume that when we buy a kg of onion, the '1 Kg' refers to its weight. However, according to the fundamental rules of physics, the combination of mass and acceleration equals weight. Basically, if we assume a 10 m/s acceleration, the mass will be 100 grams. So, did you buy 100 grams of onion or one kilogram of onion? The Unit of Weight is responsible for the entire logistics in connection to the relevance of the actual unit to represent the unit 1 kg.
On the other hand, you often label an object as heavy if you are unable to lift it off the ground? But is that all there is to the term ‘weight’? Or is there much more to it?
Also, how do we express weight mathematically? Do you use a unit of weight or mention the numerical value? Read on to find out more about it!
What is Weight?
Merely speaking, the weight of an object is the force with which the gravitational field of the Earth pulls it towards the surface. In other words, weight refers to the force at which a body accelerates towards the surface of Earth because of its gravitational pull.
As you know, anything suspended in air falls to the ground. The reason for this phenomenon is that this planet possesses a field of gravity which enables an object to fall on the ground. For instance, when you hold a ball or an egg higher from the ground level and let go of it from your hold. You witness that it immediately drops on the ground.
Therefore, the SI unit of weight aims to express the numerical value of the force that attracts an object towards the ground.
Understanding Weight
The force with which the gravitational field pulls an object towards the earth's surface is known as weight.
We're all aware that the center of gravity exerts a force that pulls all objects towards it. The numerical representation of how much force is required to force an object to reach the earth's surface is the unit of weight.
What is the SI unit of weight?
Consider that an object whose mass is 1 kg falls vertically on the ground under a gravitational force of 1 m s-2. Now, if you are wondering what is the unit of weight, it is the product of all these components.
Therefore, weight = mass X gravity.
In this case, weight of the object is –
1 kg X 1 m s-2 = 1 kg m s-2.
Thus, the standard unit of weight is kg m s-2. However, you can also express it in terms of Newton (N). This very unit calls after the famed scientist Isaac Newton who first discovered gravitational pull.
Therefore, Newton (N) refers to the SI unit of weight.
What are the Alternative Units of Weight?
Dimensional Unit of Weight – MLT-2, where M stands for mass, L refers to distance, and T is time.
CGS Unit of Weight – Dyne. CGS unit implies centimeter-gram-second, where weight becomes 1 g cm s-2. You can also arrive at dyne when you divide 1 Newton by 10000.
Base Unit of Weight – The base unit is the one that we have already discussed earlier. Therefore, it is kg m s-2.
Metric Conversion of Units of Weight
One of the most universally accepted units of weight is gram. The conversion of a gram to kilogram is based on the standard denominations, as mentioned below:
1 g = 0.001 kg
1 mg = 0.000001 kg = 0.001 g
Further, 1 centigram = 0.00001 kg = 0.01 g
1 metric ton = 1000 kg
Solve the Following Problems by Yourself
Object A has a mass of 5 kg. On the other hand, the gravity working on it is 10 m s-2. Find out what the standard unit of weight is in the case of object A.
The unit of weight in the SI system for an object X is 150 N. If the mass of object X is 50 kg, find out the gravitational pull working on it.
The gravitational force on the surface of the moon is only 1/6 as strong as the gravitational force on the earth. What is the weight in Newtons of a 10 kg object on the moon and on the earth?
Understanding Mass
The mass of an object is defined as the amount of substance contained within it. Although mass and weight have separate meanings, they are sometimes misunderstood. The quantitative measurement of inertia is what it's termed.
The mass, unlike the weight, has a fixed value that is unaffected by gravitational changes. It can be represented as a kilogram or a gram. Thus, regardless of the presence or absence of gravitational pull, a body with a mass of 70 kg on Earth will have the same mass on the Moon.
Relation Between Mass and Weight
According to Newton's 2nd Law of Gravitation, force (F) equals the product of mass (M) and rate of acceleration (rate of acceleration) (A).
F= MA
Even if the mass remains the same, the weight changes due to gravitational changes. As a result, a person's weight on Earth and on the Moon will differ significantly.
What is the Difference Between Weight and Mass?
You might often come across people who use the terms ‘weight’ and ‘mass’ interchangeably. However, these two terms have fundamental differences in what they mean scientifically. In simple terms, mass refers to the amount of matter that an object possesses.
On the other hand, weight implies the force with which the object travels towards the surface of earth. It suggests that weight differs for an object as per alterations in the gravitational pull.
For instance, the mass of an astronaut remains the same on both earth and moon. Yet, the gravitational pull is 6 times lesser on the moon than on Earth. As a result, an astronaut will weigh 6 times less on the moon than on Earth.
Now that you know what the unit of weight is, follow through the related topics to understand this concept even better. You can also download our Vedantu app to experience personalized learning online along with highly interactive sessions.
FAQs on Unit of Weight
1. What exactly is weight in Physics?
In Physics, weight is defined as the force of gravity acting on an object. It's the pull that a planet, like Earth, exerts on something. Because it is a force, its value depends on the object's mass and the strength of the gravitational field it is in.
2. What is the official SI unit used to measure weight?
The official SI unit for weight is the Newton (N). This is because weight is a type of force. One Newton is the force needed to accelerate a 1-kilogram mass at a rate of 1 metre per second squared (kg·m/s²).
3. Why do we use kilograms (kg) for weight in daily life if the SI unit is the Newton?
This is a common point of confusion. In everyday language, we use "weight" to mean mass. The kilogram (kg) is the SI unit of mass, which is the amount of matter in an object. In a scientific context, your mass in kg is constant everywhere, but your weight in Newtons changes depending on gravity. So, when a weighing scale shows your "weight" in kg, it's actually showing your mass.
4. What are the key differences between mass and weight?
While related, mass and weight are different concepts. Here are the main differences:
- Definition: Mass is the amount of matter in an object, while weight is the force of gravity on that object.
- Nature: Mass is a scalar quantity (it only has magnitude), whereas weight is a vector quantity (it has both magnitude and direction, pointing towards the center of gravity).
- Constancy: An object's mass is always the same, no matter where it is. Its weight changes based on the gravitational pull.
- Units: The SI unit for mass is the kilogram (kg), and for weight, it is the Newton (N).
5. How is the weight of an object calculated?
The weight of an object is calculated using a simple formula: W = m × g. In this formula, 'W' stands for weight, 'm' is the object's mass, and 'g' is the acceleration due to gravity at that location. On Earth, the value of 'g' is approximately 9.8 m/s².
6. How would an object's weight change if you took it to the Moon?
If you took an object to the Moon, its mass would remain exactly the same because the amount of matter inside it doesn't change. However, its weight would decrease to about one-sixth of its value on Earth. This is because the Moon has a much weaker gravitational pull than Earth.
7. Are there other units used for weight besides the Newton?
Yes, while the Newton is the standard SI unit, other units are also used. In the CGS (centimetre-gram-second) system, the unit of force and weight is the dyne. In the Imperial system, used in countries like the United States, weight is often measured in pound-force (lbf).
