What are the forces acting on ceiling fan vertically? I know that there is gravitational force acts on it downwards but what is the opposite force?
When it's off, there is only gravity pulling down, and the mount pulling up, so it remains stationary. While it is on, there is also a torque from pushing sideways through the air, which the mount must carry, and depending on the direction of rotation, also either an additional lift or downwards force from moving air down or up, respectively; this is also countered by the mount on the ceiling.
So one of the forces as you mentioned is the force due to gravity on the fan, acting vertically downwards. The other force acting vertically upwards would be the Normal Reaction Force.
You can think of the normal force kind of as tension. When you fix a string to a support with a mass attached to the free end, the tension T acts in the string, in a direction opposite to the downward force on the mass.
Also, when you place a block on a table, what is keeping the block on the table without falling through the table? It Is the Normal Reaction Force here too. If not for the normal reaction force, the block should have slid through the table.
The following forces acts on the ceiling fan according to me
Gravity, Normal reaction from the clamp, longitudinal drag due to the rotating blades, vertical lift due to the air pushed downwards, rotational friction,, Armature reaction Lastly the Electromegnetic force which is the main cause of its rotation.