Surfing the net you often happen to notice images of smoke columns getting out from volcanos and raising up to great altitudes. This is a phenomenon by many considered to be a clear evidence the Earth is not spinning. Many people could get the same impression in relation with high waterfalls: the fact that water falls on a straight line and doesn’t bend would be a clear consequence of the Earth being stationary and not spinning around its axis.
Powerful images, aren’t they? But could these phenomena show a clear evidences that the Earth is not spinning? Let’s make some consideration.
The first principle of the dynamic states: an object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an external force.
Since scientists say that Earth is set in the empty space, no external force is able to act upon the atmosphere nor consequently upon the smoke column or the waterfall.
But what about the acceleration due to rotation? Since the Earth rotates the first priciple of the dynamic is not totally applicable, due to accelerations caused by the rotation. Let’s thus calculate them.
Consider that an erupting Volcano can generate a very high smoke column. For example in 2014 the Shiveluch Volcano in Russia erupting generated a smoke column 10 km high.
Consider, to make the calculation easier, that this volcano is on the equator that means radius 6371Km and perypheral speed (at the base of the column) of 1667Km/h.
When one adds to the radius 10km, corrisponding to the altitude of the column, a speed of 1670Km/h can easily be reached.
But a 3Km difference is not very important. Consider that the wind speed increases when rising in altitude and can reach speeds much more greater than 3Km per hour. Consequently such a small variation in speed is not really evaluable, and it cannot be taken as a clear evidence of the fact the Earth is not spinning. The same reasoning can be done in the case of a waterfall.
But something different could be said when smoke is moving in a north-south direction. In this case the Coriolis acceleration should act on the column of smoke in a different, sensible way.
Looking above you have an impressive image of Eyjafjallajokull, the volcano that erupting in 2010, caused no little problems to many European airports. As shown in the picture the smoke trajectory was keeping a southward direction due to the powerful blowing of the winds. Moreover, when considering the perypheral speed of the Globe at the Iceland latitude and the one at the Italian level, a difference of at least 200Km/h could be reckoned. The smoke arrived in Italy blocking the Milan airport but you can understand that under the smoke the Earth should rotate at the incredible speed of 200Km/h.
How can a smoke column acquire the needed acceleration , reach a sufficient speed to maintain its shape in its rectilinear direction thus arriving without difficulty to cross all Europe? Moreover, consider that the Coriolis acceleration would act on the smoke column by bending it toward left, on the contrary direction seen from the image.
This rectilinear trajectory kept by the smoke, that has not been affected at all by the Earth rotation, is a clear evidence that the Earth is not spinning around its axis.