The earth attracts all bodies: people, water, seas, oceans, houses, the Moon and the Sun. However, these bodies also draw the Earth. The mutual attraction of all bodies in the universe is called gravity. The force of attraction of bodies to the planet is of primary importance to all human beings. The force, with which the earth attracts all bodies, is constantly aimed at the center of the Earth.

One experiment has established that the force of gravity is directly proportional to the body weight. If the body is at rest, the body weight is numerically equal to the force of gravity. However, one should not forget about the difference between gravity and body weight. The force of gravity is a gravitational force applied to the body, whereas body weight is a force of elasticity, applied to the support. Body weight is always equal to the force of gravity. When the body moves, its weight may increase or decrease.
Zero gravity is a state of body, at which the movement is caused only by the force of gravity. The most famous example is the weightlessness in a space ship.

The gravitation between bodies happens through space, which is not filled with any material objects. According to the materialist philosophy, the interaction between material bodies can only take material appear. In this case, such intermediary is a gravitational field. Gravitational field is a distinctive matter, with the help of which the mutual attraction of bodies takes place. Formally, the gravitational field can be defined as an area, where there are gravitational forces. However, it is essential to remember that the field is material.

The action of gravity forces in nature explains numerous phenomena: the movement of planets in the solar system, satellites, trajectory ballistic missiles, and the motion of bodies close the earth’s surface – they all can be explained by the law of universal gravitation and the laws of dynamics.
The law of universal gravitation explains the mechanical device of the solar system and Kepler’s laws describing the trajectory of the planets can be deduced from it. For Kepler, his laws had a purely descriptive character – a scientist simply summarized his observations in mathematical form and did not provide any theoretical reason. Therefore, the empirical findings obtained at a certain level can be converted to the strictly logical conclusions grounded in the transition to the next stage of deepening the knowledge about the world.