Smoke rises due to convection current. The solid particles emitted from a combustion process are carried by the hot air that rises because of its lower density than the surrounding air. The horizontal motion of smoke itself is affected by the movement of air surrounding it.
Flat-Earthers claim that a rising smoke without horizontal motion “proves” a stationary Earth. They are wrong. The horizontal motion of smoke is an effect of the horizontal motion of air relative to the smoke, and the motion of the object emitting the smoke is inconsequential.
If the air surrounding the smoke is not moving horizontally relative to the smoke, then it will not affect the horizontal motion of the smoke. The smoke will rise straight upward.
Earth’s atmosphere is stationary relative to the surface, or in other words, the atmosphere is rotating at the same speed as the rest of the Earth. Thus, we often see smoke rising straight upward, as long as it is windless, or the surrounding air is not moving.
From the standpoint of a moving steam locomotive, the surrounding air is felt moving toward the back. The reason is that the air is not moving with the locomotive, and thus, the steam & smoke emitted by the locomotive will move toward the back. However, the motion of smoke is not the result of the motion of the locomotive directly.
The claim by flat-Earthers is invalid. The fact that there is smoke rising straight upward does not prove a stationary Earth.
- Smoke – Wikipedia