Gravity and planetary motion
(one of the four fundamental forces)
gravity
The concept of gravity expresses the force that causes two physical bodies to be attracted to each other.
It is the same force that causes objects to fall
Towards the Earth and the planets revolve around the sun Gravity is one of the four main forces found in nature
The gravity of the sun keeps the Earth and all the bodies of the system in its orbit, which helps to maintain a safe and appropriate distance between them, and thus the arrival of the sun's rays with an appropriate strength to support and continue life,
The Earth's gravity also maintains the existence and cohesion of the atmosphere surrounding the Earth, which keeps us the ability to breathe and live as humans and all living creatures on planet Earth. That is the general idea of gravity.
Now let's go a little deeper:
absolute movement
Einstein, in his theory of relativity, denied the possibility of absolute motion. It is impossible to know that a body is in a state of motion or rest except by reference to another body.
Our history with the Earth’s movement confirms Einstein’s words. For centuries, we believed that the Earth was static, and this idea continued for centuries until the night Galileo looked through the telescope and discovered the Earth’s movement by observing the stars and planets around it.
But imagine if our earth was revolving alone in space, not following the sun or stars in the night sky, only darkness covered with darkness.. it would not be possible to know the movement of the earth from its stillness, and we will remain ignorant of the reality of movement, but there is only one exception.. that the earth slows down in its movement Suddenly, or suddenly speeds up, and then we realize through the gravity of our bodies and our inertia that we are on a moving object.. Like the passenger of the plane who can detect the movement of the plane without looking at the window as soon as the plane changes its speed, direction or altitude.. Or the train passenger who is sitting In a closed cabin, ignorant of the train's movement, until the train begins to slow down or deviate from its path..and realizes that his train is moving.
This simply means that motion can be absolute if it is irregular.. In this case, it can be realized by reference to itself.. without the need for an external reference.. That is why Einstein formulated his first theory, "The Theory of Relativity" and limited it to bodies that move in regular motion only. He said in it: "The laws of the universe are the same for all bodies that move in uniform motion."
But this anomaly kept haunting him.. Einstein did not believe in a complex universe, but in a simple one.. He believed that simplicity is deeper than complexity.. and that the multiplicity of laws and their contradiction in one universe indicates a superficial mathematical mind incapable of realizing the truth..
After years of thinking, it was the boldest step in Einstein's history
general relativity
In which he declared that “the laws of the universe are the same for all bodies, regardless of their states of motion.” In this way, he returned and rejected everything that is absolute.. Even the irregular motion has become relative that cannot be determined without an external reference.
gravity in space
To bring Einstein's problem to the mind of the reader, imagine Einstein's hammock tied with ropes to a vertical column.. and that this swing revolves around the column with the difference that it is completely closed.. and the one sitting inside does not see what is going on outside it.. and that it is in space away from Earth's gravity..
What will happen to a number of scientists sitting in that hammock? They will notice that their bodies are always weighted towards the floor of the hammock, and that if they throw anything, it will always fall towards the floor, and if they jump from their places, they will always fall towards the floor.. Their explanation for this phenomenon will be that there is a strong Attractiveness on this earth..
They will not be aware and will not realize that the floor of their swing is a direct external wall on space.. The reason is that their senses are always paired with any heaviness towards the floor.. Thus, all the scientists’ calculations will be certain that they are subject to the forces of gravity.. But whoever observes this swing from the outside will mistake all their calculations. He will see that they are subject to inertia known as centrifugal forces. It is the force that pushes objects moving in a circle out of the circle.
This means that there is always a possibility to confuse motion resulting from gravity and motion resulting from inertia..and it is not possible to differentiate between the two except by referring to an external reference..
Thus, there is no way to perceive absolute motion... even through irregular motion.
Thus, Einstein's theory becomes a general comprehensive for all the laws of the universe, not a theory specific to bodies of uniform motion
Gravity and Inertia
As for the second proof, Einstein takes from a well-known natural phenomenon, which is the fall of bodies towards the earth at the same speed, regardless of their mass. A ball of iron falls towards the ground at the same speed with which a ball of wood similar to it falls into the body with the same speed as a cannon bomb.
If a piece of paper falls slowly towards the ground, the reason is that its surface is large and the resistance of the air to its fall is great.. but if we turn it completely, it will fall towards the ground at the same speed as the iron ball..
This same speed with which all bodies fall was the source of a problem in nature.
The force that pushes a small ball several miles forward.
A railway wagon moves only a few centimeters, as a result of the fact that the railway wagon resists movement with its greater inertia.
Newton solved this problem with his law, in which he said:
Equivalence of gravity and inertia
The force of gravity on a body increases as its inertia increases.” Therefore, two balls of iron and wood fall at the same speed. Although the iron ball has greater inertia and greater resistance to movement, the force that pulls it is greater. Subjectivity" is another evidence of the possibility of confusion between laws..
Einstein's theory of knowledge of "general relativity" ended in denying the knowledge of everything that is absolute and considering the universe subject to one fixed laws (gravitation).
Despite the difference in motion..and to the impossibility of knowing motion from rest without a reference outside the scope of motion and the scope of stillness.
Source: websites