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| Image-National geographic |
Earth’s motions – Rotation of earth
Rotation
Rotation describes the circular motion of an object around its center. Things could have turned around in different ways.
Spinning wheel
Dora Petronzio works on a potter’s wheel in her shop in Nova Scotia, Canada. An object (such as a wheel or a planet) can rotate on its axis. Potters use the rotational motion of the wheel to ensure that their pots are level and balanced.
Rotation describes the circular motion of an object around its center. Things could have turned around in different ways.
Rotation of the earth
A very familiar type of rotation occurs when a spherical, three-dimensional object rotates around an invisible line inside its center. This center is called the axis. Spinning basketballs spin around an axis. Globes rotate around an axis. The Earth itself rotates on an axis.
Cruising
Earth’s axis is vertical, meaning it moves up and down. (A rolling log, on the other hand, has a horizontal axis, meaning it moves sideways.) Earth’s axis runs from the North Pole to the South Pole. The Earth takes 24 hours or a day to make one complete revolution around this invisible line.
As the Earth rotates, each area of its surface gets a twist and is heated by the Sun. It is important for all life on earth. The sun affects everything from the weather we experience to the food we eat and even our health. If the Earth did not rotate, one-half of the Earth would always be hot and bright, and the other half would be frozen and dark.
Rotation
The Earth also revolves around the Sun. This motion is called rotation, which is different from rotation. Objects rotate around one axis but rotate around other objects. Therefore the Earth rotates on its axis as it revolves around the Sun. Earth takes 365 days or a year to complete one rotation.
The momentum left over from when the planets were forming drives the Earth and all the planets in the Solar System to spin and orbit. As the Solar System formed, many moving particles clumped together. They formed a spinning mass. This mass eventually broke up into individual bodies—planets, moons, asteroids, and comets. All these bodies revolve around the Sun. Furthermore, all the planets, including Earth, maintained their respective rotational speeds.
The Earth rotates on its axis at a speed of about 1,600 kilometers (1,000 mi) per hour. It revolves around the Sun at a speed of 107,800 kilometers (67,000 mi) an hour.
Other types of rotation
Planets are not the only round objects that move. Amusement park rides, such as a Ferris wheel or carousel, also rotate. The Ferris wheel spins around a horizontal axis, and the carousel spins around a vertical one. The wheels of a car revolve around a strong horizontal bar called an axle. The axle runs from one side of the vehicle to the other, connecting the front wheels to each other and the rear wheels to each other.
Many household items rotate, including sprinkler heads, beaters on mixers, blades on ceiling fans, and doorknobs.
There are some things that rotate without any particular axis. Farmers use crop rotation to help the soil stay healthy and the plants get the right nutrients from season to season. Crop rotation means growing things in a different place every year. This helps prevent disease and encourages the soil to be fertilized by a variety of crops.
For example, cabbage, broccoli, and sprouts are in the same plant family. If they were grown in the same spot year after year, they could all develop clubroot disease, weakening or killing the crop and damaging the soil. The field itself acts as a spindle, with different crops being rotated at different times.
Fast facts
The tipped earth
Do you know that the earth is lying upside down? Earth’s axis is not exactly up and down. It’s actually slightly sideways, like a tipped spinning top. It is inclined at about 23.5 degrees.
How did the earth turn? Scientists aren’t sure. They think it happened when the solar system was still forming. They theorize that a massive body the size of Mars crashed into Earth, tilting it on its side.