الجاذبية - الميكانيك .. الفيزياء

Gravity - Mechanics .. Physics

Gravity

The word weight is used to refer to the force of attraction of the Earth to objects. What is gravity? Newton discovered that there are attractive forces between all material bodies that represent one of the four basic forces in the universe.

As for the other three forces, they are the electromagnetic force and the two types of nuclear forces. Although Newton did not know the cause of gravity (which Einstein later explained), he proved that it is directly proportional to the product of each of the two attracted masses, K1 and K2. And it is inversely proportional to the square of the distance between them, F. This equation was later known as Newton's law of gravity, which is as follows: F = G K1 K2/ F2, where G represents the gravitational constant (which is a quantity that does not change in all parts of the universe).

If we assume that K represents the mass of the Earth and Sh represents its radius, then its gravitational force, F, for a mass M present on its surface becomes as follows: F = G K K / Sh2, and this force is nothing but the weight of the body itself, F.

Thus, we get the following equation: F = W = K × J, where J represents the acceleration of gravity (see page 6).

We conclude from comparing these two equations that J = J K S2 and that its value is equal to J 91 m/s2. It is worth noting that this value changes depending on the location of the body and its distance from the center of mass of the Earth. If we apply the same equation to the moon, we find that there is a lunar gravitational acceleration equal to one-sixth of the acceleration of gravity on Earth, i.e. J / 6. For this reason, an astronaut on the moon can move more freely and perform giant jumps, because his weight on the surface of the moon represents only one-sixth of his weight on Earth.

It is known that every body, with a mass K, moving on a circle with a radius of length S at a constant speed V, acquires an acceleration directed towards the center of the circle resulting from the change in speed (as a vector value) despite the unchanged numerical value - i.e. the direction of the body's speed changes whenever the direction of its movement changes - this acceleration is called gravitational acceleration and is equal to V 2 / S. The attractive force becomes according to Newton's second equation. K × A = K × A2 / Sh. The attractive force has a reaction called the centrifugal force.

The moon is under the influence of two forces during its orbit around the earth: the force of its attraction towards the earth, and the force of its repulsion towards it. Since it is fixed in its orbit, these two forces must be equal. If we assume that K represents the mass of the moon, and that F represents the distance between its center and the center of the earth, we have the following equation: G K K / F2 = K A2 / F. If we replace both G and K with their values, we find that the speed of the moon's rotation is 2 × 710 / F m / s. This approximate equation (because it does not take into account the presence of other bodies in the solar system) applies not only to the moon, but to all artificial satellites, and links the distance of the satellite from the earth in its orbit to the speed of its rotation around it.

The forces that affect the motion of satellites in their circular orbits.