The question of which is heavier, iron 1kg or cotton 1kg, appears in the textbooks of primary and junior high schools. It has been stipulated that one kilogram should be taken after death, and only one kilogram should be taken under any circumstances. Its original intention is to tell students not to be deceived by their own eyes, feelings and some experiences, but to understand the relationship between quality, density and volume. If one of them is not big, the quality will be big!

From the perspective of life, although 1KG= 1KG, it seems that iron is heavier than cotton; Considering from the common sense answer, although they are all 1KG, iron is enough to kill a person, but cotton can't kill people. It seems that iron is much heavier than cotton. It is necessary to consider their density relationship.

1 kg of iron and 1 kg of cotton are mathematically the same weight. No matter which two substances are compared with each other, we only need to consider the weight, one is one kilogram and the other is one kilogram, so they are equal. From a physical point of view, cotton is heavy because the volume of the same kilogram of cotton is greater than that of one kilogram of iron, and cotton will be heavy if it loses the gravity of the earth. This is under normal circumstances, the air with large volume has great buoyancy and its weight is greater than that with small volume. Therefore, when the gravity of the earth is lost, it will become smaller.