Why is the Earth spherical and the Earth spherical?

If it weren't spherical, it wouldn't be called Earth. If it's a round cake type, it's called a floor cake.

Then why do you look like a person?

Gravitational force and centrifugal force of rotation.

The shape of the earth, as the name suggests, is "spherical" shaped. However, the understanding of the shape of the "sphere" has gone through a considerable process. Fifth and sixth centuries BC, ancient Greece.

Philosophers start from the concept that the sphere is the most perfect, and believe that the earth is spherical. Around 350 B.C., the ancient Greek scholar Aristotle.

By observing the lunar eclipse, the first scientific demonstration of the Earth's sphere was based on the fact that the Earth's shadow on the Moon is a circle. Hui Shi, a philosopher during the Warring States period in China, has long put forward the idea that the earth is spherical. Portugal in 1519.

5 sea ships led by the navigator Magellan, with 3

years, completed the first voyage around the Earth, thus directly confirming that the Earth is spherical. Since then, people have unanimously referred to the world we live in as "Earth".

The reason why the Earth is a sphere is mainly related to the rotation and gravitational pull of the Earth. Here's how it explains:

1.Gravity: The gravitational force generated by the mass of the Earth pulls towards the center of the Earth, which makes the Earth as small as possible, which is also false, that is, it turns the Earth into a sphere.

This is because in a sphere, all the points are as close to the center of the earth as possible, which is the shape with the smallest area and volume ratio of all shapes.

2.When the Earth rotates, due to the action of centrifugal force, an outward force will be generated in the equatorial part.

This causes the Earth to expand slightly in the equatorial part, forming one"Flattened spheres", that is, the Earth is actually a bystander"Ellipsoids"。The Earth's polar diameter (the distance from the North Pole to the South Pole) is slightly smaller than its equatorial radius.

These factors combine to give the Earth a roughly spherical shape. However, due to the irregularities of the earth's crust, such as mountains and trenches, the true shape of the earth is not completely smooth.

Let the Earth's rotation period be t, the Earth's radius r, and the orbital radius of the geostationary satellite r, then the satellite altitude h=r-r

The centripetal force required to make a uniform circular motion around the earth = the gravitational force of the earth:

gmm/r^2=m*a <1> a=v^2/r <2> a=r*w^2 <3> w=2π/t <4>

**Substitution formula gm=g*r 3 <5>

The following derivation can decide whether to replace the formula with ** according to the requirements of the topic<5><>

1. The sky is round.

2. According to the shape of the moon and the sun, the ancients determined that the earth is also a spherical body;

3. Magellan's first voyage determined that the earth is a sphere;

4. The satellites launched by humans take pictures in space, which confirms that the earth is a sphere.

Because the stars in the universe rely on their rotation to generate gravity to condense themselves without disintegrating, and this attraction is spherical, the sun is a star, and the gravitational force is large enough, so the spherical shape is formed according to gravity.

The gravitational pull of each celestial body is different, and the range of attraction it can attract is limited. Objects with less mass, such as comets, are often unable to form spheres because of their own gravitational pull.

The Earth is an irregular sphere with slightly flattened poles and a slightly bulging equator. This difference is very small compared to the average radius of the earth, and if you look at the earth from the universe, it can still be regarded as a regular sphere, and if you make a globe with a radius of 1 meter according to this scale, the equatorial radius is only about 3 mm longer than the polar radius, which is difficult to detect with the human eye, so it is always made into a regular sphere when making a globe.

Earth is the third planet in the solar system from the inside and outside, and it is also the terrestrial planet with the largest diameter, mass and density in the solar system, about 100 million kilometers (1 astronomical unit) from the sun.

The Earth rotates from west to east while revolving around the Sun. At present, it is 100 million years old, and there is a natural satellite - the moon, and the two form a celestial system - the Earth-Moon system. It originated hundreds of millions of years ago from the primordial solar nebula.

The reason why the earth is a sphere, the rotation of the earth, the action of gravity, the material composition of the earth, and so on.

1. The rotation of the earth.

The Earth rotates around its own axis, which makes the shape of the Earth appear similar to that of an oblate sphere. This is because the Earth's rotation speed at the equator is faster than its rotation at the poles, causing the Earth to be thrown outward at the equator, making the Earth's equatorial radius longer than the polar radius.

2. The role of gravity.

The gravitational pull of the earth causes the material on the earth to gather towards the center of the earth, which is also one of the important reasons why the earth forms a spherical shape. The gravitational pull of the earth also prevents the earth's water and atmosphere from flying away from the earth's surface and floating in space.

3. The material composition of the earth.

The material composition of the earth is also one of the reasons why the earth is spherical. The material inside the earth is made up of rocks and metals, which are subjected to high pressure and high temperature in the interior of the earth, resulting in a spherical structure.

Direction of rotation of the Earth:

The Earth's rotation axis from west to east rotates counterclockwise from the north pole and clockwise from the south pole. The Earth's axis of rotation is in the same degree as the ecliptic plane, and it is perpendicular to the equatorial plane. The Earth's rotation is an important form of motion of the Earth, with an average angular velocity of rotation in degrees and a linear velocity of 465 meters at the Earth's equator.

It takes 23 hours and 56 minutes for the Earth to rotate around and increases or decreases by 3 to 4 thousandths of a second every 10 years.

The earth rotates at the same time, and it takes 23 hours, 56 minutes and 4 seconds to rotate around in one revolution, and the revolution is about degrees, which is equivalent to 3 minutes and 56 seconds according to the speed of the earth's rotation, and the time, rotation plus the sensitive time used for revolution are 24 hours in total. Longitude is every 15 degrees, and local time is one hour apart. The rotation of the Earth also causes objects moving horizontally in any direction on Earth to deviate from the initial direction of their motion.

If the moving object is oriented in the direction of travel, the horizontal object in the northern hemisphere is biased to the right, and the southern hemisphere is biased to the left.

The above content reference: Encyclopedia - Earth.