What is the difference between mass and weight?

Probably, most often these two completely different concepts are compared, and yet they are generally taken for the same thing. Indeed, we really say: “How much do you weigh?”, when, in fact, we mean only the quantitative properties of our body, without really thinking about any other additional interactions that may imply such ambiguous word-formations. Therefore, in order not to be confused with the definitions, it is best to understand why mass cannot be weight.

Those figures that appear on the scales after, for example, they put a bag of strawberries there or tried to put a whale there, not only help determine how much money you need to pay for delicious berries or whether the whale is as big as it is said but also reveal many other features.

If we speak a scientific language, then mass is a physical value, used as a measuring unit of a body, energy, and inertness gravity, which naturally entails certain characteristics in terms of classical mechanics:

Mass (m) is invariant: this means that it doesn't depend on the choice of the reference system, for example, a passenger of a train or aircraft never loses weight drastically or gain weight during the movement of his vehicle. Such a relativity of the reference system is inherent, for instance, in determining the speed.

Mass never depends on the speed of the body movement. At the same time, inertia is the property to spend some time needed for changing the speed, is determined by the mass. The elephant, for example, cannot accelerate immediately. It will take steps that are stable and convenient for the animal, and if the mouse just sees the cat it will immediately disappear. It is less inert than the elephant, and can change its speed faster.

Also, when two bodies interact, their masses are inversely proportional to the ratio of accelerations, which is also a property of inertia. Such a discovery helped determine the planets, satellites and other astronomical bodies masses, since doing it in the other way is almost impossible.

So, let's not mix two different issues: mass and weight – the amount of a substance possessing inertia, and the force with which it is attracted by the Earth.

There are no “worlds without gravity” in nature – we could only imagine the Earth that had ceased to attract. However, in the Universe, there exist worlds of “small and large gravity” – heavenly bodies attracted with various force.

The mass of an individual on different planets remains stable, but the weight varies depending on the gravity force. That is why, for example, if the weight of astronaut is 80 kg on the earth, then on orbit it would be almost zero, on the Moon it would be less than 15 kg, but on Jupiter – almost 200 kg. However, his mass in all cases remains unchanged.

Published at 12/20/2018

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