Astronomy

Earth’s Rotation – Speed and Effect of Earth’s Rotation

Speed of Earth’s Rotation

Earth is the third planet from the sun and most dense among all. It is the only planet known to support life on it. We also call it a blue planet. Circumference of the earth is 40,232km, its area is 510 million sq. Km and its distance from the sun about 149 million km. Since Nicolas Copernicus proposed the sun-centered theory in 16th-century earth is regarded as a planet like others of the solar system. We call it the heliocentric theory. The earth is flattened a little at the poles with a slight bulge at the center. There are two types of movement of the earth. One is rotation or daily movement and other is a revolution or annual movement. Here we will discuss the earth rotation speed and its effects.

earth's rotation

Rotation of the Earth

The earth rotates around an imaginary line that passes through its north and south pole. This imaginary line is its axis of rotation. Earth rotates from west to East. Earth takes about 23hours 56minutes and 40.91seconds to complete one rotation. The rotational velocity at the equator is 1667km/hr. Its speed decreases towards the pole, where it is zero. French physicist Leon Foucault is credited for measuring the speed of earth’s rotation.

Effects of Rotation of the Earth

The spinning of the earth on its axis causes days to turn into nights. A difference of one hour is created between two meridians which are 15 degrees apart. A change in the direction of wind and ocean currents. The rise and fall of tided every day.

1. Effect on the Direction of the Wind

The wind is the movement of air in a particular direction. Its principal cause is pressure difference. In addition, the rotation of the earth also affects the direction of the wind. When the earth rotates on its axis, wind cannot move in a straight line toward north and south from the equator.

A Coriolis force is generated. Under its influence, winds deflect to their right in the northern hemisphere and to their left in the southern hemisphere. This is referred to as Ferrel’s law. Coriolis force is absent at the equator and increases towards the pole. This Coriolis force creates a global pressure belt which defines the weather of the earth. Let us see some effects in different regions of earth.

  1. Doldrums: Present from 5°N of the equator to 5°S. The centrifugal force is high at the equator, where the velocity of rotation is high. Hence, air masses tend to throw out, resulting in low pressure. Here wind speed is low. Most calm area of the earth.
  2. Horse latitudes: Located from 30ºN to 30ºS of the equator. Here pressure depends on the rotation of earth and movement of air. Winds from the doldrum belt rise up and accumulate here.
  3. Trade winds:- Due to the Coriolis force, they blow from North-East in the northern hemisphere to the south-east in the southern hemisphere.
  4. Easterlies and Westerlies:- Easterlies are deflected by the earth’s rotation to become east winds while the westerlies blow from the west in the northern hemisphere.

2. Cyclones

Due to earth’s rotation cyclones move in an anticlockwise direction in the northern hemisphere and in a clockwise direction in the southern hemisphere.

3. Ocean currents

Because the ocean current is driven by the movement of wind earth’s rotation also affects the direction of the movement of ocean current. The spiraling pattern on the current is due to the Coriolis effect. In the northern hemisphere current move towards right while in the southern hemisphere towards left.

4. Change of day and night

Earth rotating on its axis is the reason behind days and nights every 24 hours. If the earth does not rotate day/night cycle would be nonexistent. As the earth is tilted 22½° on its axis this causes the difference of longer and shorter days. When the difference is largest we call it solstice. When days and nights are equal we call it equinox.

Question on Earth Rotation Speed

Q – What will be the effect of the earth’s rotational speed is increased?

Ans – Days and night will become shorter, as it will take less than 24 hours to complete a full rotation by the earth. Because of faster speed, centrifugal force will increase and gravity will remain constant. Thus, our weight will decrease. There will be temperature change as the earth’s hemisphere will have less time to warm up.

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