Tuesday , October 26 2021

Could the Moon really crash to Earth?


With a push in the opposite direction, the angular momentum decreases. This means that the overall turnover rate is reduced. The moon does not stop making a total orbit, but now it orbits slowly enough because it acts more like a rock falling to Earth and almost hitting it.

(Yes, in the illustration they seem to collide, but remember I made the Earth and the moon bigger than they should be so they could see them. Actually, it would be more of a fault).

The best way to make the Earth and the Moon fall would be to completely freeze its orbit or, in physical terms, decrease the speed of the Moon to zero (relative to the Earth). Once the moon stops orbiting, it would only fall directly on the planet, because the Earth’s gravitational force will stretch on it and cause it to increase in speed as it moves toward the planet. This is essentially the same as dropping a rock on Earth, except that it is much larger than a film could be made about it.

To achieve this, you will need a larger “mysterious” force or a push for longer. (If there are aliens reading this, please do not use it as a plan to destroy the Earth.)

Could the Moon separate the oceans from the Earth?

But a shock is not the only way the moon can bring us down. At one point in the trailer, it appears that the moon is so close that its gravitational force drives the ocean away from the planet’s surface. Could this really happen?

Let’s start with the simplest case, where the moon and Earth are stationary and almost moving. It would be like this:

Illustration: Rhett Allain

Now suppose I put a one kilogram water ball on the surface of the planet. Because water has mass, it has a gravitational interaction with the Earth, throwing water toward the center of the Earth. But there is also a gravitational force from the moon that pulls in the opposite direction. What force would be greater?

We can calculate them with the same universal gravitational force for the moon’s orbit. For the interaction with the Earth, we will use the mass of the Earth and the mass of water. (I took 1kg to make it easier.) The distance (r) will go from the center of the Earth to the surface, it is only the radius of the Earth. For the interaction with the moon, I will use the mass of the moon and the radius of the moon (plus a little more, as they don’t touch each other at all).

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