Question

When we see any object through the hot air over the fire, it appears to be wavy, moving slightly. explain?

Answer 1

 It is the hot air! Fire creates a sort of blanket of hot air around itself and outside that is the cold air. The former one has a tendency to lift upwards, while that of the latter one is to come down. The hot air around the object rises, and cold air fills up the emptied space. This cool air again gets warmed, rises, and then replaced by the cold one. This process continues until fire blows out

Answer 2

Explanation:

The objects beyond the hot air appears to be wavy because the medium for light to pass through  changes, the light passes from denser to rarer and then again to denser medium thereby causing refraction  in the air. Moreover the refractive index of the hot air keeps changing which leads to give the wavy  appearance of the object.