Physics trivia

# Why doesn’t the moon fall to Earth?

Why doesn’t the moon fall to Earth? The explanation for this lies in the speed of the Moon’s rotation around the Earth.

The Moon is Earth’s only natural satellite and is at a distance of approximately 380,000 km. By having a period of rotation similar to the period of translation, only one face of the satellite is visible from Earth . The star, which does not produce its own light, but reflects the light of the Sun , has four distinct phases and orbits the Earth at an approximate speed of 3700 km/h.

With an equatorial diameter of approximately 3500 km, the Moon has a mass of 7.35 x 10 22 kg, and the acceleration due to gravity on lunar soil is 1.6 m/s 2 . A good question about this satellite is why does it just not fall? How does the Moon keep revolving around the Earth?

## Newton responds!

Isaac Newton, in the 16th century, imagined the possibility of placing any objects in orbit around the Earth, an idea that explains how the Moon is kept in its trajectory without falling on our planet.

Newton observed that, when throwing a stone with a certain horizontal velocity, the trajectory of the object makes a parabola until it reaches the ground. This happens because the Earth’s gravitational force on the stone pulls it towards the ground. Each time the launch speed is increased, the object reaches greater distances, so the English physicist imagined that there must be a sufficiently large speed capable of causing the launched object to rotate around the Earth and return to its initial position. .

## Why doesn’t the moon fall?

The Moon’s rotation speed around the Earth keeps it in an infinite fall motion around the planet, so the moon never hits the Earth’s ground. The movement of the Moon encounters no resistance in space , as it occurs in a vacuum, the speed is maintained and our satellite will always remain in orbit.

## What should be the speed of a satellite?

From the centripetal force equations and the definition of the law of universal gravitation , we can determine the speed required for a satellite to be in orbit. This speed depends on the mass of the orbiting planet and the distance between the planet and the satellite.

The terms of this equation are:

V: Satellite speed;

G: Universal gravitation constant (6.7 x 10– 11Nm2/Kg2);

M: Earth Mass (approximately 6.0 x 1024Kg);

A: Distance from the satellite to the center of the Earth.