What are the forces acting on a floating balloon

The basic aerodynamic forces are lift, drag, thrust and weight.

Weight is the force generated by the gravitational attraction of the Earth on an object. For a floating balloon, weight is a force which is always directed towards the center of the Earth. The magnitude of this force depends on the mass of the balloon and its payload (instruments and containers). For the balloon to float a force must be generated to overcome weight. This force is called lift. Lift is caused by the buoyancy of the balloon. Buoyancy is an upward force caused by a difference in density between two fluids. In the case of a balloon, the two fluids are air and helium. Since helium is much less dense than air, a given volume of helium is less dense than the same volume of air. The heavier air exerts an upward force on the balloon causing it to rise. Once the balloon is floating, it is moved horizontally by the force of thrust. For a balloon, thrust is supplied by blowing wind. As the moving air strikes the surface of the balloon, it propels the balloon forward. As the balloon moves forward, the still air directly in front of the balloon pushes against the balloonand resists the movement of the balloon. The resistant force is called drag. In order for the balloon to move forward, the force of thrust must be greater than the force of drag.

The forces acting on a floating balloon are ;
1) weght of the balloon including its contents = W, acting downwards
If the Total mass of the ballon and its contents is M and W = its total weight then W = Mg
2) Buoyancy of the medium (air) in which it is floating = w, acting upwards.
Since the balloon is completely immersed inside air the buoyancy or the up thrust is equal to
the weight of the displaced air.
V = external volume of the ballon and d = density of air, then w = V d g
3) The wind force driving it in the direction of the wind

The basic aerodynamic forces are lift, drag, thrust and weight.