A word about the scalability of ideas concerning collisions.
As the mass of two objects increases, ones intuition as to their behavior decreases.
For example; if you put two apples side by side, nothing much happens.
However, if you put two planets side by side, then they pull each other together and reshape themselves into a single (spherical) planet. Something that apples certainly do not do.
Another example; if you have two apples collide (in space) at 3 km/s, they explode into little pieces.
However, if two planets collide (in space) at 3 km/s, they once again pull each other together and reshape themselves into a single (spherical) planet and there is essentially no splatter.
The reason for this Newton's law of gravity.
Newton's law of gravity, states that the gravitational force F between two masses m_1 and m_2, at a distance r, is
F = G * m_1 * m_2 / r²
where G is the gravitational constant.
Suppose that m_1 and m_2 are two single atoms, at a distance r from each other, and that the gravitational force between them is one unit.
Now increase both m_1 and m_2 to ten atoms, still at distance r, then the gravitational force between them is not ten units, but one hundred units.
This is because, for a fixed distance of separation, the gravitational force of attraction between two objects, is proportional to the product of their masses.
Now suppose the mass of an apple is 0.2 kg and the mass of the Earth is 5.97369 x 10^24 kg.
Then Earth is roughly 3 x 10^25 times as massive as the apple.
If the force between two apples, at a distance r from each other, is
z,
then the force between two Earth's, at a distance r from each other, is
900000000000000000000000000000000000000000000000000 * z
i.e., 9 x 10^50 times as strong.
This is the reason that things that might happen to two apples are usually quite different from things that might happen to two planets.
