• Weight

 

Weight results from the gravitational thrust exerted by the Earth on any body on its surface. This force is applied on the gravitational center of the body. Its direction is the vertical line going through the center of the Earth. Thus, weight is a force exerted from a distance. 

 

Its formula is P = m.g, where g is acceleration on the Earth surface, approximately equal to              , and m the mass of the body in kg.

 

The gravitational force is a constant, noted G equal to                     expressed in 

 

 

• Archimedean force

 

For a more detailed presentation, see the devoted article (go to Archimedean buoyant force)

 

Archimedean buoyant force = P(fluid)xVxG (fluid density (kg/cm3) x immersed volume (m3) x gravity force G (N/kg))

 

 

• Upward thrust

 

The upward thrust has the same orientation as the weight and Archimedean force, a reverse direction from the weight and with the magnitude equals to the difference of the two former forces.

 

It is the thrust that enables the balloon to stay in the air. 

 

 

• Assessment on forces

 

FA and FP forces compensate each other. 

 

Two forces compensate each other if and only if they have:

          - The same length

          - The same orientation

          - A reverse direction

 

In physics, forces are represented by a vector.