# How do you differentiate between pressure and gravity

## Basics of gravity

### Discovery of gravity

In the Middle Ages it was believed that the earth in the centre of the universe and both the sun and the other planets around the Earth circle. This is known as that geocentric worldview. But astronomers kept looking up at the sky and watching them Movements of the celestial bodies and their orbits. With increasing knowledge about the planetary orbits, however, it became more and more difficult to explain the geocentric view of the world. Johannes Kepler it was finally the three in 1615 Kepler's laws set up and so that heliocentric worldview established, according to which the focus is not on the earth but the sun and all planets in Circular or elliptical paths circle around it. As you now know, Kepler was right then. He didn't know though Why the planets revolve around the sun.

Sir Isaac Newton, a British physicist, also formulated some mathematical and physical laws like that in the 17th century calculus, which is usually the subject of mathematics class in high school, and the three Newton's lawsthat you already know from mechanics. Isaac Newton also discovered the Gravity. According to legend, he got the brilliant idea when an apple fell on his head and he wondered why the apple fell under at all, even though nobody bumped it. You've probably heard this story before. But did you also know that same Force, which is responsible for the fact that the apple fell on Newton's head, is also the reason that the planets orbit the sun? If not, you feel like many people in the 16th and 17th centuries. But with Newton's description of gravity, both could be explained.

### The law of gravitation

The Gravity is one of the four basic physical forces. Although it is the weakest of all four forces, it is the only force that has an influence on something as large and heavy as planets, stars or entire galaxies. The gravity, too Gravity called, is a force between two or more Masses works. Gravitation always works attractive, never repulsive. This is what distinguishes them from the electromagnetic force that acts between two magnets, for example. Ever greater the mass of an object is, the more stronger is its gravity. That means that not only the sun and the planets have a gravity, but also the moon, humans, apples and even the smallest particles and atoms. Everything that has a mass exerts a force of gravity. For example, this is only much smaller on the moon than on earth, which is why the astronauts were able to make such big jumps on the moon. An apple's gravity is much smaller, however Not zero.

Newton also discovered that the force of gravity with increasing distance weaker becomes. This means that the further two masses move away from each other, the weaker they attract. So if you rock yourself once on the ground until you weigh heavier than if you rock yourself on top of a mountain. After all, you are further away from earth on the mountain. The difference in weight is of course very small, but if you increase the distance even further and you move further and further away from the earth, you will eventually become weightless be.

The exact Law of gravitation between two masses \$ m_1 \$ and \$ m_2 \$, which are at a distance of \$ r \$, reads:

\$ F_G = -G \ frac {m_1 m_2} {r ^ 2} \$.

\$ G \$ is a Natural constant. Incidentally, there are two masses in the formula. This means that the force that you exert on the earth is just as great as the force that the earth exerts on you. Of course you don't notice anything about the fact that you can attract the earth, otherwise it would “come after you” when you jump into the air. This is not because you are exerting less gravity on the earth, but only because the earth is much smaller acceleration learns.

### ebb and flow

Perhaps you have asked yourself by now what role gravity plays for you in everyday life, apart from the fact that it lets things fall to the ground. Gravity is responsible for ebb and flow. It is mainly the moon that, with its gravity, controls the Masses of water the seas attracts and since water is free to move, you see tide on the beaches of this earth. The tides are created by an interaction of the Gravitation of the moon, the Centrifugal force due to the rotation of the earth around its own axis. Also the Gravity of the sun plays a role, even if it's only a minor one.