Tags – Difference between mass and weight


When you hear the terms weight and mass, they seem to be interchangeable every time they’re discussed, yet they’re anything but!

Nevertheless, the two terms are in fact proportional to each other, i.e. if you know the mass (m) of something, you can calculate its weight (w) as w=mg g=9.8 N/kg.

I know, this looks very confusing. But in this case, g represents the local gravitational field, where everything on the earth’s surface has a proportional constant of 9.8.

To put it simply, the difference between mass and weight is that mass measures the amount of matter in any given object whereas weight is a measure of the effect of gravity on that mass – gravity causes a mass to have weight.

To break the equation from earlier down, weight = mass x gravity.

Let’s take a look at what mass and weight are separately in a bit more detail.


What is Mass?

Mass measures how much matter an object is made from, and is usually measured in grams or kilograms.

To put it differently, if you’re able to add up all the number of protons, neutrons and electrons (and other subatomic particles) that make up an object, this would be mass.

Mass is connected to force, and it can also be measured by calculating the amount of force needed to change the direction or speed of an object. You may be familiar with the equation: F (force) = M (mass) x A (acceleration).

In addition, mass is also linked to gravity, which is the attraction between two objects that have mass depending on the distance.

With that said, they are not related – gravity has no effect on mass.

Plus, mass is indestructible and can never be equal to zero. Because, if mass measures how much matter is in an object, then how can an object be made up of zero matter?


What is Weight?

Weight then, is actually measured in newtons, not grams.

And the imperial unit for weight is the pound.

Now remember how we said earlier that mass and gravity are linked? Well, weight is the gravitational interaction between objects that have mass.

For example, you may have heard something about mass on earth and mass on the moon being the same, but you’ll weigh less on the moon than you do on earth. And that’s because the gravity is not the same.

Unlike mass, weight can be equal to zero, but this depends on gravity.


So Why Is There Confusion?

Ok, so we know mass and weight are not only related but are proportional to one another.

As such, if you know something’s weight, you can calculate its mass and vice versa, using the equations mentioned above.

Because we live on Earth, we can use these terms interchangeably. It’s not like you need to consider mass on another planet, unless you’re a scientist of course.

Not only that, but referring to weight in newtons would create a lot of confusion for most people. For instance, if I was to say my dog weighs 45kg, you’d know he’s a pretty big dog. But if i said he weighs 445 newtons, this wouldn’t mean anything!


Scales, Mass and Weight

Scales give you the weight of something.

But if we’re going to be technical, it actually measures how much force is exerted on the load cell, and then uses gravity to give your mass.

A scale cannot measure mass directly. The reason being is that the weighing mechanism and the weight in an object are dependent on gravity.

When it comes to weighing large objects, such as a lorry, they can be driven onto a weighbridge, which is supported by hydraulic rams. As the lorry drives onto it, force is applied on the rams and they have to push upwards to balance its weight – the weight is then calculated from the hydraulic pressure.

So just to clarify, scales measure how something weighs by measuring the force applied. And even though it’s force that’s calculated, it’s presented in measurements of mass, i.e. kg or lb, which is why it can get confusing (as explained above).

However, because of this crossover, using the two terms interchangeably will always be accepted.


Please get in touch to find out more.

In the meantime, take a look at our Vehicle Weight Checker solutions


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