Surfing the net you often happened to notice images of smoke columns getting out from volcanoes and raising up to great altitudes. This is a phenomenon that many people consider to be 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.
A waterfall or maybe a smoking volcano are powerful images. But could these phenomena show any clear evidence 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 believe 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 principle of the dynamic is not totally applicable, due to the 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, generated a smoke column 10 km high. Consider, to make the calculation easier, that this volcano is, just to give an example, on the equator, that means radius of the Earth 6378 km and peripheral speed (at the base of the column) of 1669,3 km/h (this should be the speed of the rotating Earth at the equator).
When one adds to the radius 10 km, corresponding to the altitude of the column, a peripheral speed of 1671.8 km/h can easily be reached (remember the formula to calculate the peripheral speed).
But a 2–3 km/h difference is not very impressive. Consider the fact that the wind speed increases when rising in altitude and that it can reach speeds much more greater than 3 km 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 could
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 differently sensible way. The Eyiafjallajokull is the volcano that erupting in 2010 caused no little problems to many European airports. The smoke trajectory was keeping a southward direction due to the powerful blowing of the winds.
Moreover, when considering the peripheral speed of the Globe at the Iceland latitude and the one at the Italian level, a difference of at least 200 km/h could be reckoned. Anyway, the smoke column arrived in Italy blocking the Milan airport, but, as you can remember, under the smokescreen, the Earth in Italy was rotating at the incredible speed of 1200 km/h. (In Island the approximate peripheral speed is 1000 km/h).
How can a smoke column acquire the needed acceleration, reach a sufficient speed to maintain its shape in its rectilinear direction, arriving thus to cross all Europe without difficulties? Moreover, consider that the Coriolis acceleration would act on the smoke column by bending it toward left, on the opposite direction. This is due to the fact the Earth should rotate towards east and the smoke should remain back at west.
This rectilinear trajectory followed by the smoke, without being affected at all by the Earth rotation, is a clear evidence that the Earth is not spinning around its axis. The rotation of the Earth should have an influence on the winds too. Think of the trade winds that blow from tropics toward the equator. These winds blow in direction north–south.
Remember that the Coriolis Effect can act only on a body moving in this direction. A helicopter that moves only in an east–west direction is not affected by Coriolis. These winds are originated by the hot air warmed by the sun at the equator latitudes. The warmed currents ascend pulling thus air from the tropics. Science says that these winds blow in an oblique direction due to the Coriolis Effect.
But, when trying to make a research, you will find that these winds blow at an average speed, during the year, of about 18 km/h. Moreover, at the tropics the Earth peripheral speed should be of about 1530 km/h, while at the equator the Earth spins at about 1670 km/h. This means that trade winds should blow at the good speed of about 140 km/h, that is the difference between the two before mentioned speeds.