The Difference Between Mass and Weight

Although many people use the words ‘mass’ and ‘weight’ interchangeably, they are not the same thing!



However, the two terms are proportional to each other, meaning if you know the mass (m) of an object, you can then calculate the weight (W) as 

W=mg g=9.8 N/kg. 

In this case, g represents the local gravitational field, and so this calculation only works for those of us on the Earth's surface, where there is a proportional constant of 9.8 kilograms.  

So, for most of us who have no plans to leave the planet, the two can mean basically the same thing. But, what exactly is the difference between mass and weight? 

What is Mass?

Essentially, the mass is how much stuff (or matter) is in an object. It may not be possible, but if you could count up the total number of protons, neutrons and electrons that make up an object then this would be a measure of mass. 

Kilograms and grams are common units used for mass, although the imperial unit for mass is the ‘slug’. 

Mass has a connection with Force, as it can be measured by calculating the amount of force required to change the direction or speed of an object. 

F (force) = m (mass) x a (acceleration) 

Mass is also linked to gravity, which is essentially the attraction between two objects that have mass depending on the distance. However, gravity has zero effect on mass. It is also important to note that, like energy, mass is indestructible and can never be equal to zero as it is impossible for an object to be composed of zero matter. 

What is Weight?

Gravitational interaction occurs between objects that have mass. The force of an object interacting with the earth is known as weight. 

Just like other forces, the unit used for weight is the Newton, although the imperial unit for weight is in ‘pounds’. 

If you were to land on the moon, your mass would be the same as it is on Earth. However, you would weigh less on the moon, as its mass is not the same as Earth’s mass. Therefore, its gravity is not the same. Unlike mass, weight can be equal to zero depending on the force of gravity. 

What is the Difference Between Mass and Weight?

Mass is the quantity of matter in a body, and weight is the force by which the earth attracts towards its centre. 

Mass is a scalar quantity, meaning it can be described by its size or magnitude only, and weight is a vector quantity meaning it has both a size or magnitude as well as a direction (towards the centre of gravity). 

The mass of a body is constant everywhere in the universe, whereas the weight of a body will vary becoming zero at the centre of the earth and far away from its surface. 

There are a number of formulas used to calculate mass as it is always a constant for a body. One formula is: 

Mass = volume x density 

Simply put, weight is the measure of gravitational force acting on a body and can be calculated using the following formula: 

Weight= mass x acceleration due to gravity   

The formula for working out the Mass of a moving object is M=F/A 

The formula for working out the weight of an object is W=mg 

Mass can be determined by an ordinary balance but the weight of a body is measured by a spring balance. 

The International System of Units (SI) measures mass in kilograms (kg) and weight in Newtons (N). 

Mass, Weight & Weighing Scales

Weighing scales provide you with an accurate weight reading of an object. However, as you will be aware we don’t usually weigh items in Newtons, for example, you wouldn’t say your cat weighs 42 Newtons. 

What weighing scales actually do is measure how much force is applied onto the load cell and then uses gravity to calculate your mass. 

At Marsden, we have supplied reliable and accurate weighing scales to both the UK and the wider world for over 90 years. Our products are designed for a range of purposes including medical scales, industrial scales, veterinary scales and gym & fitness scales. 

To find out more about any of our Marsden Weighing Scales or to discuss a bespoke weighing solution contact the team today on +44 (0) 1709 364296 or email sales@marsdengroup.co.uk.  

Further Reading

We sell a wide range of weighing scales across the UK and around the world, take a look at these seven uses of a weighing scale.

Have you ever wondered how do Weighing Scales work?

<How do you weigh a lorry?

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