What is the difference between body mass and weight? We are always wrong

In everyday life, we use the term “weight” to describe the amount of matter contained in an object. This popular confusion is reinforced by the fact that the weight of an object is used to measure its mass.

In this confusion, two terms coexist in our vocabulary: mass and weight. We tend to use one or the other as we please, when they are actually two very different concepts. This is why sometimes we not only find ourselves confused, but we can also confuse the other. In fact, to be honest, we’re sure more than once while using them, you’ve remembered that you weren’t quite clear regarding them, so just so you don’t forget, we We will explain here what each of them is.

On the one hand, mass is a unit of measurement that refers to the amount of matter present in an object. It is usually expressed in kilograms (kg) or grams (g). It is a quantity fixe“, that is to say that it does not depend on the position or the speed of the object.

Weight, on the other hand, measures the force that gravity exerts on an object. In this case, it is therefore directly linked to the position of the object in space. It is usually expressed in newtons (N) or kilogram-force (kgf) and can be calculated by multiplying the mass of the object by the force of gravity.

A constant error

However, in everyday life, the term “weight” is most commonly used to describe the amount of matter an object has. This is, as you have seen, a cultural misunderstanding, a popular confusion reinforced by the fact that the weight of an object is often used to measure its mass.

Indeed, when we use a scale to measure the weight of an object, we are actually measuring the force exerted on the object, and this depends on gravity. If we take the example of a space traveler visiting the different planets of the solar system, the question would be:

Suppose that on Earth the person weighs 70 kilograms. Whatever happens, the amount of matter contained in this person (that is, its mass) will remain unchanged. On the other hand, its weight will vary according to the celestial objects that it visits.

A simple examples

So, on Mercury, its weight would be 27.3 kg, since on this planet the force of gravity is different from that acting on Earth, namely regarding 0.38 g. If you were on Venus, you would weigh 68 kg (the force of gravity there is 0.9 g).

On the outer planets, in fact, the weight would be much higher: on Jupiter, which has a gravity of 2.5 g, it would weigh 243 kg. On Saturn, it would weigh regarding 94 kg, with a gravitational force of regarding 1 g. On Uranus, it would reach 87 kg (in this case, the gravity is 0.9 g).

Note, however, that these examples do not take into account the environmental conditions inherent to each planet, such as atmospheric pressure, temperature and weather conditions, which can also influence the measurement of weight.

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