# What is gravity really?

## Gravity

Gravity is the force that the Earth exerts on all bodies, attracting them to its center. It is gravity that causes objects to fall to the ground and creates the sensation of weight. It is also responsible for all the movements we observe in the universe.

The force that keeps you down to earth and in its most literal sense, no figurations. Basically, this is the idea we all represent when we think about what gravity is.

Image by mohamed Hassan from Pixabay

Although the Italian scientist Galileo Galilei was one of the first to investigate what caused the movement of objects, it was not until Isaac Newton studied”gravity” that we began to understand this characteristic of the universe.

We will know what causes gravity, what its theory is and even some curiosities. We will travel from Aristotle to Newton.

## Definition of Gravity

From the Latin gravĭtas, gravity is a physical force that the Earth exerts on all bodies towards its center. It is also the force of attraction of bodies by virtue of their mass.

Besides, it’s the force with which bodies attract each other. Basically, it is the force that acts to prevent us from floating and from remaining attached to the Earth.

One of the effects of this phenomenon is to slow down anybody we throw upwards. In fact, it creates the opposite effect when the object stops and starts to fall.

In this case, gravity will be able to attract it to Earth at a faster rate.

It is also linked to weight, which is the force of gravity exerted by the mass of the planet on all objects within its gravitational field.

The weight of the same body may vary on different planets if its mass is different from the mass of the Earth.

### Early Theories of Gravity.

Since antiquity, man has sought answers to doubts that have arisen through observation and knowledge.

Since the dawn of human history, man has known that objects are attracted to the ground. Simply, with observation, you come to that knowledge.

In the fourth century BC, the philosopher Aristotle developed his theory on the relationship between the causes and effects of these causes.

His theory holds that everything that happens must have a cause. Thus, he maintained the existence of an invisible force that draws us to the center of the universe.

Bearing in mind, of course, that the Earth was the center of the universe and everything revolved around it.

The first name this force received was Gravitas. His theory contained some flaws such as believing that there was a different gravity depending on the mass of the body.

Thus, two different bodies, with different masses, are attracted with different forces by gravity.

### Copernicus S’s Theory

Copernicus provoked a real reaction in the society and sciences of the 16th century. The Sun was the center of the universe.

As we have seen so far, the Earth was the center of the universe. A truth accepted and supported by religious beliefs that dominated all aspects of society.

Copernicus was not aware of the extraordinary size of the universe. In fact, it focused on the Solar System, the only thing known about astronomy at the time.

This theory could amend the first mistake that the philosopher Aristotle had made.
This theory disturbed a Church that remained convinced that man, God’s creation, was the center of the universe.

If the Earth is not the center of the universe, Aristotle’s entire gravitational theory would fall apart. Now the Earth is no longer the center of the universe, but we are still attached to it. That is, the Earth exerts the force responsible for things falling.

### Theory by Galileo Galilei XVI – XVII A.D.

Galileo was a man of mathematical vocation, despite his father’s efforts to make him study medicine. Interested in the fall of bodies, he began to conduct experiments on the fall of objects in inclined planes.

Thus, he concluded that gravity was a constant force in all bodies, thus correcting another of the errors of Aristotle’s theories.

It is said that he spent many, many hours experiencing it from the Tower of Pisa. In it, he tried to measure the time it took for an object to touch the ground.

In the churches, he used to do calculations to measure the pendular movement of the censers.

### Kepler’s Theory of XVI-XVII A.D.

Johannes Kepler was a Protestant pastor who believed in God, but also a firm follower of Copernicus’ theory.

With a different interpretation of God’s creation, where the duty of the good Christian is to try to understand and know the work of God, and of course the solar system was a work of God.

In this way, he helped the work of Copernicus and Galileo to cross the borders of Catholic Europe, and to become known and accepted in Protestant Europe.

He described it as a complex system created by God to keep the planets spinning.
Among his works are the three laws describing, with great precision, the motion of planets spinning in elliptical orbits.

The most widespread theory to be able to answer all these questions was based on the existence of two gravity forces.

One that affects Earth’s objects. Another one that seems to be a celestial force that gets the planets spinning.

### Gravity according to Newton

The English physicist, mathematician, philosopher, and inventor Sir Isaac Newton proposed the law of universal gravitation or theory of gravity.

Newton stated that every object possessing mass exerts a gravitational pull on any other object with mass, beyond the distance between the two.

The greater the mass, the greater the force of attraction; on the other hand, the closer the objects are, the greater the force of attraction.

However, we must not forget the fact that throughout history there have been other scientists and researchers who have also left their mark on the term gravity.

This would be the case, for example, of the German physicist Albert Einstein who is known precisely for his theory of general relativity.

### Gravity according to Einstein

In 1915, the German physicist Albert Einstein presented his theory of general relativity to the scientific community, which we could basically say is a reformulation of the term.

Einstein hypothesizes that space and time were one and that they served as the fabric of the universe.

He established that gravity was a simple curvature in space-time, created by an object with a much greater mass than the surrounding objects, which could cause them to fall on top of this higher density object.

### Newton’s Law of Universal Gravitation

It is a mathematical way of describing how bodies attract each other, that is, how gravity works between bodies.

The gravitational equation shows that the force of gravity is proportional to the product of two masses (m1 and m2) and inversely proportional to the square of the distance (r) between their centres of mass. Thus, from the point of view of mathematics, we see it that way:

F=Gm1m2 / r2,

G is the gravitational constant and has a value of 6.6726 x 10-11 m3 kg-1 s-2. The effect of gravity then extends from each object in space in all directions and at an infinite distance.

However, it is important to note that the force of gravity decreases easily and quickly as the distance increases.

None of us is aware of the force of gravity that the Sun exerts on our planet and this is due to the short distance that exists between the Earth and the great star.

However, that force is the one that keeps our planet orbiting in the Solar System and it is the same force that keeps the Moon orbiting the Earth.

We are also not aware of lunar gravity, but we can appreciate its behaviour if we take into account its effects on tides.

### What is the center of gravity?

The center of gravity is defined as the point of application of the resultant of all the actions of gravity on the particles that make up a body.

This point is different in each body and its position is constant, whatever the sense, direction and orientation to which the body is subjected. It’s as if all the body weight is gathered at that point.

### What is Acceleration of Gravity

If a body falls towards the Earth, the body’s rate of fall increases as it approaches the Earth’s surface.

It is then said that the movement of the body is an accelerated movement. This action of gravity is called the acceleration of gravity, and its symbol is usually the letter g.

Acceleration is the increase in speed in m/s at every second of movement, i.e. meters/second².

Meanwhile, the acceleration of gravity increases as it passes from the equator to the poles, just over 5% of its speed.

The normal acceleration gn ,i.e. the acceleration at 45° north latitude and sea level, makes it possible to establish gravity as a function of a unit of force.

### What is Zero Gravity?

This concept refers to the condition in which gravity appears to be absent. As such, it occurs when the weight of a body is counterbalanced by another force, thus balancing the gravitational forces, which can occur as a result of the acceleration of a body in orbit or in free fall.

Thus, the zero gravitational situation can be experienced during a free fall or in a spacecraft. The permanence in this state, on the other hand, is called weightlessness.

### Is there gravity in space?

Of course, of course! Gravity is everywhere. The effect decreases with distance, but it never goes away.

So the term “zero gravity” is an inappropriate name. What really happens to astronauts (or satellites) is that they fall `sideways’ towards the planet, which keeps them in orbit and with a feeling of not having weight.

Where the space station orbits, at about 400 kilometers in height, the force of gravity is about 90% of what it is here on the surface.

### Curiosities

There are curiosities about gravity that you may not be aware of.

How much would it weigh on another planet?. We’re used to Earth’s gravity, but what if we went to another planet? If it is Jupiter, a person weighing 75 kg will weigh more than 160 kg.

On the other hand, if that planet is Pluto (although since 2006 it is no longer a planet, a dwarf planet), that same person would barely reach 5 kilos of weight.

### For example

Returning astronauts – When astronauts return from space, they have to go through a time of adaptation to get used to the Earth’s gravity again.

This is because there is no gravity in the space, the muscles become numb and the blood pressure has to work with less intensity.

Floating I Go – On the other hand, when returning to Earth, astronauts who have spent a lot of time in space must become accustomed, when returning to Earth, to the fact that objects do not float.

Strong and weak – Gravity is one of the strongest and weakest laws. On the one hand, they have great force and importance since absolutely all objects on Earth are governed by these laws

On the other hand, it is one of the weakest forces, since with a simple electromagnetic magnet you can attract an object overcoming the force of gravity of the Earth.

Hudson Bay – Gravity is not the same everywhere on Earth and can vary from area to area.

For example, it has been found that Hudson Bay has less gravity than the rest of the planet.

### Earth

Scholars believe this may be due to the existence of ancient glaciers in the area. These glaciers, thousands of years ago, crushed the Earth, reducing its mass.

Attraction, yes; repelling, no – Yes, gravity is a force capable of attracting bodies to the planet, but it is not capable of doing the opposite, that is, it cannot repel bodies.

Escape speed – How much speed is needed to escape the gravity field? To escape the force of gravitation and get out of the planet into space, it is necessary to reach a minimum speed of 11.26 kilometers per second.

Pens in space – As the last curiosity, I would like to mention that pens do not work in gravity. To solve this, some companies have made special pens for space.

Like the one who patented a company called Fisher Pen Company in 1965 and who could also write underwater.