What is the weight: how and why it occursfor gaseous matter

A pure mechanical approach is proposed to gain a more penetrating insight into the physical meaning of the body’s weight, in deducing its notion just from the Newton’s equation for the body moving along the gravitational field. In that view, the body is weighty when its acceleration along the g-field is other than g. The approach was used for to account the occurrence of the gaseous matter weight that was regarded by us as some sort of experimentum crucis capable of estimating its validity. According to the results obtained, the body’s weight is a physical reality fundamentally different from the force of gravity, and represents the inevitable factor assuring the fulfilment of the momentum conservation law in the body – Earth system.