Can the Moon Fall to the Earth?
With a push in the opposite direction, the angular momentum decreases. This means that the overall rotation rate decreases. The moon does not completely stop orbiting, but now it is orbiting so slowly that it moves like a rock that has fallen to Earth and almost hit it.
(Yes, in the illustration they seem to collide – but remember I made the Earth and the moon much larger than before so you could see them.
The best way to break up the Earth and the moon is to completely freeze its orbit, or in physics terms, to reduce the speed of the moon to zero (relative to the Earth). When the moon stops orbiting, it will actually fall to the planet, because the gravitational force from the Earth will pull it and cause it to increase in speed to get to the planet. This is the same reason as dropping a rock on the Earth, except that it’s so much more that you can make a movie about it.
To accomplish this, you need more “mysterious” force or a push for a longer time. (If there are any aliens out there reading this, please don’t use it as a blueprint for destroying Earth.)
Can the Moon Take the Seas of the Earth?
But collapse isn’t the only way to break us on the moon. At one point in the trailer, it looks like the moon is so close that its gravitational force is pulling the ocean away from the planet’s surface. Is that really possible?
Let’s start with the simplest case, where the moon and Earth are moving and almost touching. As such:
Now imagine I put a 1 kilo ball of water on the surface of the planet. Because water has mass, it has a gravitational interaction with the Earth, pulling water toward the center of the Earth. But there is also a strong gravitational force from the moon pulling in the opposite direction. Which force is more numerous?
We can calculate the same using the same universal gravitational force for the moon’s orbit. For Earth interaction, we will use a lot of Earth and the mass of water. (I chose 1 kg to make it simpler.) The distance (r) from the center of the Earth to the top-that is the only vicinity of the Earth. For the lunar interaction, I will use the mass of the moon and the radius of the moon (add a little more because they are less touching).