The rotation of the Earth is the rotation of the Earth around its axis. The time of one rotation is 23 hours 56 minutes and 4 seconds and corresponds to one stellar day ( a stellar day – the time between two highs of the vernal equinox point). A day, however, is called the time that elapses between two consecutive sun rises over a given meridian ( solar day). The solar day lasts 24 hours. Rotational motion is from west to east, that is, in the opposite direction to the Sun’s apparent motion across the celestial vault. As a result of the rotational motion, the Earth’s surface is unevenly illuminated. The illuminated hemisphere is daytime, while the unlit hemisphere is nighttime.
The reason for the rotational motion is also the flattening of the Earth at the poles, that is, the difference between the polar and latitudinal radii. The flattening of the Earth is about 21 km. The speed caused by rotational motion varies throughout the globe. The highest linear velocity of moving points is observed at the equator and is 1670 km/h. As one moves away from the equator, this speed decreases. At the 50° parallel it is already 1104 km/h, and at the poles it is 0 km/h. Symptoms of deflection of bodies in motion can be found in the shifting of air masses. As a result of the uneven heating of the Earth’s surface, a global air circulation is formed.
On a globe that would not perform rotation, these shifts of atmospheric air masses should take place in a meridional direction. As a result of rotation, and the action of the Coriolis force, deviations from the meridional directions of the tracks of a body moving, along the Earth’s surface, toward the equator in a westerly direction in both hemispheres, and in an easterly direction when the body moves toward either of the poles, i.e. toward the axis of rotation, are created at the Earth’s surface. The discoverer of the Coriolis force was French mathematician Gaspard-Gustave Coriolis. The Coriolis force is expressed by the formula:
А= 2 ω υ sinφ
where:ω – angular velocity of the Earth’s rotation
υ – speed of motion of the particle
φ– latitude
The diurnal rotation of the globe also causes falling bodies to deviate from the vertical direction to the east. At high altitudes, and with accurate determination of the direction of the plumb line, the deviation can be easily observed. Such an experiment was performed in the early 19th century by dropping appropriate weights from church towers. For example, in 1802, with experiments performed in Hamburg, a deviation of 9 mm was obtained from a church tower 73 meters high. According to calculations, the deviation should be 8 mm. Another evidence of rotational motion is the changes in the value of the Earth’s acceleration depending on latitude.
This is because the body moving closer to the axis of rotation retains a greater linear velocity. North of the equator, this force causes the trajectory of moving objects to curve to the right (from the point of view of the moving object), while to the south it curves to the left. This effect is not usually felt, and manifests itself only in the case of prolonged processes or in the case of bodies moving freely over a large area. In the northern hemisphere, the wind tends to turn to the right, while in the southern hemisphere it tends to turn to the left. Also, the right banks of rivers occurring in the northern hemisphere are more strongly washed up, while in the southern hemisphere they are left. In the northern hemisphere, cyclones move counterclockwise, while in the southern hemisphere they move clockwise.
Rotational motion also causes the movement of tidal waves caused by the gravitational interaction of the sun and moon. Over almost the entire globe except the polar regions, rotational motion causes a diurnal change in illumination, i.e. the succession of day and night, and a diurnal rhythm of changes in the Sun’s height above the horizon. Evidence of the Earth’s rotational motion is Foucault’s Pendulum-it is a pendulum that was constructed in 1851 by Jean Foucault. It was shaped like a long eleven-meter pendulum suspended in the Pantheon in Paris This pendulum has the ability to swing in any plane. By setting it in motion, it should maintain its direction.
However, it turns out that the pendulum does not change its plane of oscillation only at the equator. The plane of oscillation of the pendulum in Foucault’s experiment changes uniformly with respect to the Earth making a rotation from east to west. Numerous witnesses could see that the line drawn by the direction of the pendulum slowly rotated relative to the floor and walls of the Pantheon. In fact, the Pantheon rotated along with the Earth, while the direction of oscillation remained unchanged thanks to the phenomenon of inertia. The angular velocity of rotation of this pendulum’s plane of oscillation depends on the latitude of the place where the experiment is performed. At the equator, the plane of oscillation of the pendulum does not change The change in the plane of oscillation is caused by the rotation of the Earth around its axis.
