Only one force acts on a body that moves around the Earth - this is the gravitational force of our planet. The object will move unevenly and unevenly. This is because acceleration and speed in this case will not satisfy the conditions for uniform / uniformly accelerated movement with a constant speed / acceleration in direction and magnitude. These two vectors (speed and acceleration) as they move in orbit will always change their direction. Therefore, such a motion is sometimes referred to as a motion with constant speed in a circular orbit.
The first cosmic is the speed that must be given to the body in order to bring it into a circular orbit. In this case, it will become like an artificial satellite of the Earth. In other words, the first cosmic one is speed, having reached which a body moving above the Earth’s surface will not fall on it, but will continue to move in orbit.
For the convenience of calculations, this motion can be considered as occurring in a non-inertial reference frame. Then the body in orbit can be considered as at rest, since two forces will act on it : centrifugal and gravity. Therefore, the first cosmic velocity will be calculated based on the consideration of the equality of these two forces.
It is calculated by a certain formula, which takes into account the mass of the planet, body mass, gravitational constant. Substituting the known values into a specific formula, one gets: the first cosmic velocity - 7.9 kilometers per second.
In addition to the first cosmic, there are second and third speeds. Each of the cosmic velocities is calculated according to certain formulas and is interpreted physically as the speed at which any body launched from the surface of the planet Earth becomes either an artificial satellite (this will happen when the first cosmic velocity is reached) or leaves the Earth's gravitational field (this happens when second cosmic velocity), or leave the solar system, overcoming the attraction of the sun (this happens at the third cosmic velocity).
The spacecraft, having gained a speed equal to 11.18 kilometers per second (second space), can fly toward the planets in the solar system: Venus, Mars, Mercury, Saturn, Jupiter, Neptune, Uranus. But in order to reach any of them, one must take into account their movement.
Previously, scientists believed that the motion of the planets is uniform and occurs around the circumference. And only I. Kepler established the true shape of their orbits and the pattern by which the speeds of celestial bodies change as they rotate around the Sun.
The concept of cosmic velocity (first, second or third) is used in calculating the motion of an artificial body in the gravitational field of any planet or its natural satellite, as well as the Sun. So you can determine the cosmic velocity, for example, for the Moon, Venus, Mercury and other celestial bodies. These speeds should be calculated using formulas that take into account the mass of a celestial body, the gravitational force of which must be overcome
The third spacecraft can be determined on the basis of the condition that the spacecraft must have a parabolic trajectory in relation to the Sun. To do this, during launch at the surface of the Earth and at an altitude of about two hundred kilometers, its speed should be equal to approximately 16.6 kilometers per second.
Accordingly, cosmic speeds can also be calculated for the surfaces of other planets and their satellites. So, for example, for the Moon, the first space will be 1.68 kilometers per second, the second - 2.38 kilometers per second. The second cosmic velocity for Mars and Venus, respectively, is 5.0 kilometers per second and 10.4 kilometers per second.