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Returning to the example of an item dropped from the ceiling of a plane - yes, the momentum transferred to it by force of gravity balances instantaneously, by third law. It balances by accelerating the item, in free fall, by second law.
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No.
The momentum is not "balanced by the item accelerating".
Gravitational attract is occuring between two masses, one very big (the Earth) and one very small (the item you dropped). So, not only is the item accelerated towards the earth, but an equal and opposite gravitational attraction (Newton 3) is pulling the Earth towards the item. As a result, both accelerate towards on another.
However, since the Mass of the Earth is very very Huge, the resulting acceleration (newton 2) is very small. The item though has a much smaller mass and therefore accelerates a lot more.
Newton 3 tells us the gravitational attraction is equal and opposite.
Newton 2 tells us each item experiences a rate of change of momentum equal to the force.
The upwards momentum of the earth is equal in size to the downwards momentum of the item at all times. Added together as vectors they cancel one another out, and the total vertical momentum of the item and the Earth is zero, at all times.